James C Baygents

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• Sounart, T. L., Safier, P. A., & Baygents, J. C. (2005). Theory and simulation of isoelectric focusing. Elsevier Inc.. doi:10.1016/s0149-6395(05)80006-6
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  IEF is an electrophoretic process that hinges on the mobility versus pH behavior of ampholytes. The basic theory of IEF tells us that separands focus about their pI in a Gaussian distribution. Peak height and variance depend on the competition between diffusion away from the pI and electromigration towards it. Comprehensive simulations of IEF involve the numerical solution to conservation laws for all the relevant amphoteric and ionogenic species in the separations milieu. The conservation relations are non-linearly coupled to the driving electric field and through the complicated mass-action relations. With the increased speed of microprocessors, one-dimensional simulations of the type shown here are now readily managed. The simulations offer the possibility of gaining insight into the detailed dynamics of the unfolding separations process. To see a more comprehensive exposition of IEF simulation results, particularly with regard to pH gradient development, the reader should refer the monograph by Mosher et al. © 2005 Elsevier Inc.

Journals/Publications

• Baygents, J. C., Chen, Y., Farrell, J., & Gervasio, D. (2021). Factors Affecting Hydroxide Ion Concentrations in Bipolar Membranes. Journal of Membrane Science and Research, 7(Issue 4). doi:10.22079/jmsr.2021.521613.1433
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  The useful lifetime of bipolar ion exchange membranes is often limited by nucleophilic attack by hydroxide ions on the ionic groups and polymer backbone in the anion exchange layers (AELs). This is especially problematic in water treatment applications for making acid and base from salt solutions. This research investigated the effect of bulk electrolyte composition, current density, membrane thickness, ion exchange capacity, and bulk solution pH value on hydroxide ion concentrations inside the AELs of a bipolar membrane. One-dimensional Nernst-Plank equations were solved for the species Na+, Cl-, OH- and H+ within 20-100 µm thick anion and cation exchange layers with fixed charged densities ranging from 0.5-2.0 eq/L. In 1 M NaCl solutions at neutral pH values, hydroxide concentrations in the AEL reached as high as 2.2 M at a current density of 100 mA/cm2. In 1 M NaOH solutions, hydroxide ion concentrations reached as high as 3.77 M. Hydroxide concentrations in the AEL were significantly affected by the ratio of Cl- to hydroxide ions in the bulk electrolyte. Where hydroxide concentrations in the bulk electrolyte were an order of magnitude lower than chloride concentrations, membrane hydroxide concentrations were nearly proportional to the current density. Increases in ion exchange capacity and AEL thickness resulted in increased membrane hydroxide ion concentrations. Membrane concentrations of hydroxide ions can be minimized by operation at low current densities, with high background electrolyte concentrations using thin membranes with low ion exchange capacities and producing base concentrations less than 0.1 M.
• Baygents, J. C., Chen, Y., Farrell, J., Gervasio, D., & Martinez, R. J. (2020). Alkaline Stability of Novel Aminated Polyphenylene-Based Polymers in Bipolar Membranes. Journal of Membrane Science and Research, 6(2), 218-225. doi:10.22079/jmsr.2019.115517.1298
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  This research investigated stability of two novel aminated polyphenylene polymers as anion exchange layers in bipolar membranes. Bipolar membrane stability was tested under operating conditions of 50 mA/cm2, and under conditions of soaking in room temperature 1 M NaOH. The stability of the custom made bipolar membranes was compared with those for two commercial membranes. For the polyphenylene-based membranes, there was no measurable increase in operating voltage when run continuously at a current density of 50 mA/cm2. For the two commercial membranes, the operating voltages increased by 3.2 to 4.4 mV per day when operated continuously over an 85 day testing period. Commercial membrane degradation in 1 M NaOH was similar to that under real operating conditions, with average rates of voltage increase of 3.2 to 3.5 mV/d. The custom made membrane containing a quaternary ammonium-tethered poly(biphenylalkylene) (PBPA) anion exchange layer did not show any loss in performance in either stability test. Density functional theory (DFT) simulations were used to calculate activation barriers and reaction energies for nucleophilic attack on the polymer backbones and cation functional groups on each of the four anion exchange polymers. Cation loss from all four polymers was thermodynamically favorable, with activation barriers ranging from 64 to 138 kJ/mol. The two commercial polysulfone-based anion exchange membranes were susceptible to cleavage of the ether bonds. However, the polyphenylene-based anion exchange polymers were considerably more stable with respect to backbone cleavage. The DFT calculations showing that the PBPA polymer was the most stable confirmed the results of the stability tests.
• Baygents, J. C., Chen, Y., Farrell, J., Gervasio, D., & Martinez, R. J. (2020). Water splitting promoted by electronically conducting interlayer material in bipolar membranes. Journal of Applied Electrochemistry, 50(1), 33-40. doi:10.1007/s10800-019-01365-4
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  Bipolar membranes are used in a variety of industrial applications to split water into hydronium and hydroxide ions. This research investigated the hypothesis that an electronically conducting material between the anion and cation exchange membranes can increase the rate of water splitting by increasing the electric field intensity in the mobile ion depleted region. Bipolar membranes were constructed with electronically conducting (graphene and carbon nanotubes) and electronically insulating (graphene oxide) interlayer materials of varying thickness. All three interlayer materials decreased the voltage required for water splitting compared to a bipolar membrane with no interlayer material. Quantum chemistry simulations were used to determine the catalytic effect of proton accepting and proton releasing sites on the three interlayer materials. Neither graphene nor carbon nanotubes had catalytic sites for water splitting. Thicker layers of graphene oxide resulted in decreased rates of water splitting at each applied potential. This effect can be attributed to a diminished electric field in the mobile ion depleted region with increasing catalyst layer thickness. In contrast, membrane performance with the electronically conducting graphene and carbon nanotube interlayers was independent of the interlayer thickness. An electrostatic model was used to show that interlayer electronic conductance can increase the electric field intensity in the mobile ion depleted region as compared to an electronically insulating material. Thus, including electronically conducting material in addition to a traditional catalyst may be a viable strategy for improving the performance of bipolar membranes.
• Baygents, J. C., Chen, Y., & Farrell, J. (2017). Evaluating electrocoagulation and chemical coagulation for removing dissolved silica from high efficiency reverse osmosis (HERO) concentrate solutions. Journal of water process engineering, 16(Issue), 50-55. doi:10.1016/j.jwpe.2016.12.008
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  Abstract High efficiency reverse osmosis (HERO) produces high pH concentrate streams that often contain high levels of dissolved silica. Removal of silica from these concentrate streams is desirable before brine concentration and crystallization. This research investigated removal of dissolved silica from simulated HERO concentrate solutions using electrocoagulation (EC) with mild steel anodes and chemical coagulation with FeCl3. At pH values of above 10, the mild steel anodes immediately passivated and were not able to deliver Fe2+ ions into the solution. This necessitated lowering the solution pH value via HCl or FeCl3 addition prior to EC. At pH values ≤10, iron dosing by EC was in agreement with that given by Faraday's law. The optimal initial pH value for operating the EC process was 8, which required addition of 17.8 mM HCl or 5.8 mM FeCl3. An EC iron dose of 4.0 mM resulted in 76–89% silica removal for solutions with initial pH values between 4 and 8. Higher dosing up to 9.3 mM increased silica removal by only 5%. Chemical coagulation was not as effective as EC, and was able to achieve a maximum removal of 64% with a 4.0 mM FeCl3 dose. Solution ionic strength had no measurable impact on silica removal by EC, but did affect final solution pH values and silica removal by chemical coagulation. For both EC and chemical coagulation, the initial pH value of solution had greater impact on silica removal than the iron dose.
• Baygents, J. C., Chen, Y., & Farrell, J. (2017). Removing phosphonate antiscalants from membrane concentrate solutions using granular ferric hydroxide. Journal of water process engineering, 19(Issue), 18-25. doi:10.1016/j.jwpe.2017.07.002
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  Abstract Phosphonate antiscalants are commonly used in membrane desalination to prevent fouling by mineral scale. In many circumstances, it is desirable to remove these compounds before concentrate disposal or further treatment. The goal of this research was to determine if the kinetics of phosphonate adsorption and desorption from granular ferric hydroxide (GFH) are sufficiently fast for GFH to be used in packed bed adsorption systems for antiscalant removal from membrane concentrate solutions. Well-stirred batch experiments were performed to investigate the adsorption kinetics of Permatreat 191 ® (PT191) and nitrilotri(methylphosphonic) acid (NTMP) onto GFH. Uptake of both compounds was slow and continued over the course of 6 days. Adsorption isotherms measured after 24 h elapsed showed initial concentration effects, whereby the isotherms were dependent on the initial adsorbate concentration in solution. This can be attributed to chemical adsorption reactions with faster rates of bond formation than bond breaking. Strong phosphonate adsorption in high pH solutions and high activation barriers for desorption resulted in slow kinetics for adsorbent regeneration by NaOH solutions. Desorption rates were bimodal, with 40–50% of the adsorbed phosphonate being released on a time scale of 10–24 h, while the remaining fraction was released approximately one order of magnitude more slowly. Complete regeneration could not be achieved, even after eluting the adsorbent columns with more than 300 bed volumes of 1.0 mol/L NaOH. The inability to regenerate the adsorbent in an efficient manner likely precludes its use for cost-effective antiscalant removal from membrane concentrate solutions.
• Baygents, J. C., Chen, Y., & Farrell, J. (2017). Understanding Competitive Adsorption of NTMP and Silica on Ferric Hydroxide. Environmental Engineering Science, 34(6), 401-409. doi:10.1089/ees.2016.0441
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  Ferric hydroxide adsorbents are commonly used to remove phosphonate antiscalants from membrane concentrate solutions. This research investigated competitive adsorption of nitrilotris(methylenephosphonic acid) (NTMP) and silica on ferric hydroxide. Equilibrium adsorption isotherms were measured and column breakthrough and regeneration experiments were performed for an NTMP adsorbate in simulated membrane concentrate solutions with and without dissolved orthosilicic acid. Quantum chemistry simulations using density functional theory (DFT) were used to evaluate the thermodynamic favorability of possible adsorption mechanisms for NTMP and silica. Column breakthrough experiments showed that 86 mg/L of dissolved silica decreased adsorption of NTMP by 36% after 3,685 bed volumes. DFT modeling indicated that NTMP and silica adsorption on ferric hydroxide may occur through both mono- and bidentate complex formation. NTMP adsorption through a bidentate binuclear complex was 12 kcal/mol more energetically favorable than monodentate complexation. Dimerization reactions between adsorbed silica and dissolved silica greatly increased silica adsorption for dissolved silica concentrations greater than 60 mg/L. DFT modeling and experimental results also indicated that dissolved NTMP may react with adsorbed silica through condensation reactions. Although adsorbed silica decreased the total uptake of NTMP, it increased the efficiency of regeneration by 0.10 M NaOH solutions. This is consistent with adsorbed silica decreasing formation of bidentate binuclear NTMP complexes.
• Baygents, J. C., Chen, Y., Davis, J. R., Farrell, J., & Nguyen, C. H. (2016). Electrochemical Ion-Exchange Regeneration and Fluidized Bed Crystallization for Zero-Liquid-Discharge Water Softening.. Environmental science & technology, 50(11), 5900-7. doi:10.1021/acs.est.5b05606
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  This research investigated the use of an electrochemical system for regenerating ion-exchange media and for promoting the crystallization of hardness minerals in a fluidized bed crystallization reactor (FBCR). The closed-loop process eliminates the creation of waste brine solutions that are normally produced when regenerating ion-exchange media. A bipolar membrane electrodialysis stack was used to generate acids and bases from 100 mM salt solutions. The acid was used to regenerate weak acid cation (WAC) ion-exchange media used for water softening. The base solutions were used to absorb CO2 gas and to provide a source of alkalinity for removing noncarbonate hardness by WAC media operated in H(+) form. The base solutions were also used to promote the crystallization of CaCO3 and Mg(OH)2 in a FBCR. The overall process removes hardness ions from the water being softened and replaces them with H(+) ions, slightly decreasing the pH value of the softened water. The current utilization efficiency for acid and base production was ∼75% over the operational range of interest, and the energy costs for producing acids and bases were an order of magnitude lower than the costs for purchasing acid and base in bulk quantities. Ion balances indicate that the closed-loop system will accumulate SO4(2-), Cl(-), and alkali metal ions. Acid and base balances indicate that for a typical water, small amounts of base will be accumulated.
• Baygents, J. C., Chen, Y., Davis, J. R., & Farrell, J. (2015). Production of Acids and Bases for Ion Exchange Regeneration from Dilute Salt Solutions Using Bipolar Membrane Electrodialysis. ACS Sustainable Chemistry & Engineering, 3(9), 2337-2342. doi:10.1021/acssuschemeng.5b00654
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  The acids and bases used for ion exchange regeneration contribute significantly to the increasing salinity of potable water supplies. This research investigated the use of bipolar membrane electrodialysis (BMED) for producing acids and bases from dilute salt solutions that are produced during reverse osmosis or evaporative cooling. Using single pass BMED, acids and bases were produced with concentrations equal to ∼75% of the feed salt concentration with current utilizations >75%. Current utilization increased with increasing feed salt concentrations due to decreased leakage current through the monopolar membranes. The maximum current density at which the BMED stack could be operated depended on the feed salt concentration and the flow velocity and was limited by water dissociation at the interface between the diluate solutions and the monopolar membranes. The stack resistance was dominated by the bipolar membranes, even for the most dilute feed solutions. The energy required per mole of acid or base produ...
• Baygents, J. C., Chaplin, B. P., Farrell, J., & Hubler, D. K. (2014). Understanding Chlorite and Chlorate Formation Associated with Hypochlorite Generation at Boron Doped Diamond Film Anodes. Journal of The Electrochemical Society, 161(12), E182-E189. doi:10.1149/2.1001412jes
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  This is a copy of an article published in the Journal of The Electrochemical Society © 2014 Electrochemical Society Publications.
• Baygents, J. C., Chaplin, B. P., Farrell, J., & Hubler, D. K. (2014). Understanding Chlorite, Chlorate and Perchlorate Formation When Generating Hypochlorite Using Boron Doped Diamond Film Electrodes. ECS Transactions, 58(35), 21-32. doi:10.1149/05835.0021ecst
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  This research used density functional theory for investigating reactions on boron doped diamond (BDD) film electrodes that contribute to unwanted byproduct formation during hypochlorite generation. Clusters containing 10 carbon atoms were used to simulate the diamond electrode surface. The simulations included reactions with hydrogen terminated surfaces, and with surface sites produced by anodic polarization, namely: ≡C•, =C•H, ≡C-O• and =CH-O•. The activation energies for oxidation of chlorine oxyanions via direct electron transfer and via reaction with hydroxyl radicals were calculated. Oxychlorine radicals (ClO•, ClO2 •, ClO3 •) were found to chemically adsorb to both secondary and tertiary carbon atoms on the BDD surface. These chemisorbed intermediates could react with hydroxyl radicals to regenerate the original chlorine oxyanion (ClO−, ClO2 −, ClO3 −), and produce ≡C-O• and =CH-O• sites on the BDD surface. The ≡C-O• and =CH-O• sites also reacted with oxychlorine radicals to form chemisorbed intermediates, which could then be converted to higher oxidation states (ClO2 −, ClO3 −, ClO4 −) via reaction with hydroxyl radicals.
• Baygents, J. C., Davis, J. R., & Farrell, J. (2014). Effect of current density and sulfuric acid concentration on persulfuric acid generation by boron-doped diamond film anodes. Journal of Applied Electrochemistry, 44(7), 841-848. doi:10.1007/s10800-014-0692-0
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  This research investigated the effects of current density and sulfuric acid concentration on the rates of persulfate generation by boron-doped diamond film anodes. Also investigated was the maximum conversion of sulfate to persulfate that could be achieved from electrol- ysis of sulfuric acid. Experiments were performed in batch systems using a rotating disk electrode (RDE) and a flow- through reactor with parallel plate electrodes. Both the RDE and flow-through experiments showed that there was a linear relationship between persulfate generation rates and current density. Persulfate generation rates became current limited at sulfuric acid concentrations of 2.25 M and above; however, Faradaic efficiencies under current- limited conditions were only *60 %, and were only weakly dependent on the current density. Persulfate gen- eration rates in the flow-through reactor showed similar dependencies on current density and sulfuric acid concen- tration as those in the RDE reactor, but were 20-50 % lower. Acid catalyzed and thermal decomposition of per- sulfate limited the maximum conversion of sulfate to per- sulfate. A maximum fractional conversion of 78 % was achieved using an initial sulfuric acid concentration of 0.77 M. Surprisingly, this value was independent of the current density over the range of 100-300 mA cm -2 .
• Baygents, J. C., Davis, J. R., & Farrell, J. (2014). Understanding persulfate production at boron doped diamond film anodes. Electrochimica Acta, 150(Issue), 68-74. doi:10.1016/j.electacta.2014.10.104
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  Abstract This research used molecular modeling and rotating disk electrode experiments (RDE) to investigate possible reaction pathways for persulfate production via electrolysis of sulfuric acid solutions using boron doped diamond (BDD) film anodes. Density functional theory (DFT) modeling indicated that uncatalyzed oxidation of SO 4 2− and HSO 4 − occurs at lower potentials than water oxidation, and that sulfate radical species (SO 4 −• and HSO 4 • ) may be produced via direct electron transfer, or via reaction with hydroxyl radicals. The RDE experiments indicated that rates of persulfate generation were strongly dependent of the condition of the electrode surface, and that aged electrode surfaces favored water oxidation over direct SO 4 2− and HSO 4 − oxidation. Combination of sulfate radical species in solution is the lowest energy pathway for persulfate production. Sulfate radical species may also react with radical sites on the electrode surface and produce chemisorbed intermediates that can stabilize sulfate radical species. Reaction of the chemisorbed intermediates with a bisulfate radical can produce persulfate via a surface catalyzed pathway. However, the activation barriers for this pathway are much higher than those for persulfate production via solution phase species.
• Hunter, J., & Baygents, J. C. (2013). Grand challenges DELI (Discover, Explore, Learn, Imagine) project update. ASEE Annual Conference and Exposition, Conference Proceedings.
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  Abstract: Here we report on data collected for a project in which five new web-based lines of study, referred to as Elective Units, were developed by engineering faculty members with expertise in topics related to the NAE Grand Challenges.1 In a previous communication,2 we described the rationale, development scheme and topical content of the Elective Units. In this work we summarize selected results for the first full-scale offering of the Elective Units to a large cohort of students (400+) enrolled in an undergraduate engineering program. The Units were designed to give freshmen and prospective engineering students, many of whom are still in high school, an opportunity to explore topics of their choice in the engineering foundation course, Introduction to Engineering, offered by the University of Arizona (UA). The selection of topics was based on a Grand Challenges Interest Survey administered to 100+ freshmen engineering students, as part of the groundwork for the project. Students participating in the Interest Survey were asked to investigate the fourteen Grand Challenges for Engineering established by the National Academy of Engineering and indicate which challenges captured their interests. The five new Elective Units were modeled after a pilot Unit that was developed and successfully delivered in Spring 2010 as a result of a Learner-Centered Course Redesign Innovation Grant, funded by the Arizona Board of Regents. The learning in the Units is experiential in that each Unit allows students to address, first-hand, various types of problems that engineers attempt to solve. The activities require students to use a variety of tools to investigate the topics in order to establish a foundation of knowledge. Students are encouraged to further investigate topics and make connections to the societal, global, environmental and economic context that frame the Grand Challenge. The assignments are designed to motivate students to engage in higher-level thinking. Vignettes, i.e. short videos, describing each challenge and emphasizing the important role that engineers play in solving these challenges, were recorded. In addition, detailed written descriptions of the Units were developed. Students use the vignettes and reference materials to decide which Elective Unit(s) they wish to study. They then have the opportunity to devote four weeks of the semester, roughly one Carnegie unit of effort, to the exploration of the topic by making use of the cyberinfrastructure. © American Society for Engineering Education, 2013.
• Baygents, J. C., Dakubo, F., & Farrell, J. (2012). Hydrogen Peroxide Removal From Chemical–Mechanical Planarization Wastewater. IEEE Transactions on Semiconductor Manufacturing, 25(4), 623-629. doi:10.1109/tsm.2012.2205283
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  The goal of this paper was to identify and investigate a practical method for removing hydrogen peroxide from wastewater generated during chemical and mechanical planarization of integrated circuits. Rates of hydrogen peroxide destruction were investigated using: 1) ultraviolet (UV) light; 2) electrochemical reduction and oxidation; 3) two activated carbon catalysts; and 4) a pyrolusite catalyst. The effects of ethylenediaminetetraaceticacid (EDTA), ethylenediamine (ED), and dissolved copper ions on rates of ${\rm H}_{2}{\rm O}_{2}$ destruction were also investigated. Hydrogen peroxide destruction rates using UV light and the electrochemical reactor were too slow to be useful in a practical treatment scheme. Both activated carbon and pyrolusite catalysts produced fast rates of ${\rm H}_{2}{\rm O}_{2}$ destruction. However, the presence of EDTA and ED decreased reaction rates on activated carbon, whereas rates on pyrolusite were unaffected. Column experiments with the pyrolusite yielded greater than 99.9% ${\rm H}_{2}{\rm O}_{2}$ destruction using empty bed contact times as short as 1 min.
• Baygents, J. C., Dakubo, F., & Farrell, J. (2012). Peroxodisulfate assisted leaching of chalcopyrite. Hydrometallurgy, 121(Issue), 68-73. doi:10.1016/j.hydromet.2012.04.004
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  Abstract This research investigated the effectiveness of peroxodisulfate (S 2 O 8 2− ) for enhancing copper leaching rates from chalcopyrite. Batch and column experiments were performed using sulfuric acid leach solutions at pH = 2, with and without Na 2 S 2 O 8 . The presence of peroxodisulfate greatly increased copper leaching rates. Tafel analysis and electrochemical impedance spectroscopy experiments performed using chalcopyrite powder electrodes indicated that peroxodisulfate increased the corrosion rate by decreasing the charge transfer resistance for chalcopyrite oxidation. In contrast to the preferential leaching of iron that has been observed for other oxidants added to chalcopyrite leach solutions, peroxodisulfate assisted leaching resulted in the release 1 mol of Cu per mole of Fe, which is identical to their stoichiometric ratio in chalcopyrite. Rates of Cu leaching from chalcopyrite followed a surface reaction rate limited, shrinking-core model with an apparent activation energy of 41 kJ/mol.
• Baygents, J. C., Farrell, J., & Hubler, D. K. (2012). Sustainable Electrochemical Regeneration of Copper-Loaded Ion Exchange Media. Industrial & Engineering Chemistry Research, 51(40), 13259-13267. doi:10.1021/ie301443u
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  An electrochemical method for regenerating copper-loaded ion exchange media was investigated. The method involved circulating a moderate pH regenerant solution between a bed of ion exchange media and an electrochemical cell. The electrochemical regeneration process eliminates more than 99% of the acid and base use associated with conventional regeneration, consumes no water, produces metallic copper, and eliminates the production of a copper-laden sludge. Experiments were performed measuring copper plating rates as a function of the aqueous copper concentration, cell current, and flow rate. Experiments were also performed to determine the equilibrium partitioning of copper ions between the solution and the ion exchange media under loading and regeneration conditions. A mathematical model was developed and calibrated using experimental data, to provide guidance for the design of electrochemical ion exchange regeneration systems. The model incorporates the plating kinetics, the stripping of copper from the resin, and the equilibrium isotherm and predicts aqueous and adsorbed copper concentrations during the regeneration process. The model indicates that, in 789 min, 90% of copper can be removed from a resin loaded with 50 mg(Cu)/g(resin). An economic analysis indicates that energy costs for plating are less than 1% of chemical costs for conventional ion exchange regeneration.
• Baygents, J. C., Farrell, J., Hubler, D. K., Mackay, C., & Megdal, S. B. (2012). Evaluating economic effects of semiconductor manufacturing in water-limited regions. Journal American Water Works Association, 104(2), 47-48. doi:10.5942/jawwa.2012.104.0024
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  High-volume semiconductor manufacturing (HVSM), with its associated high demands for freshwater, is often located in regions with limited water resources. This nexus of water demand and scarcity has generated concerns among municipal governments, prompting several to consider water supply restrictions as they plan for economic growth and development. By assessing water use data and economic valuations of land use from Chandler, Ariz., this study compared the economic benefit of HVSM with three alternative water uses: office, retail, and general manufacturing. Normalizing the economic benefit to net water use (after reclamation) had a marked effect on the fiscal consequences of water uses. The effects generated by mostly nonconsumptive water uses (such as HVSM and general manufacturing) increased significantly relative to less waterintensive, but more consumptive, water uses. Results showed that water-intensive land uses need not be avoided in communities where water is scarce, provided the community has the facilities necessary to reclaim the wastewater.
• Hunter, J., & Baygents, J. C. (2012). Grand Challenges Deli (Discover, Explore, Learn, Imagine) project. ASEE Annual Conference and Exposition, Conference Proceedings.
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  Abstract: In Fall 2011, researchers in the College of Engineering at the University of Arizona received an NSF Transforming Undergraduate Education in STEM (TUES) grant to develop learner-centered materials and strategies for an existing engineering course required of entry-level students. The strategy for the project, named the GC DELI (Grand Challenges: Discover, Explore, Learn and Imagine), is to give freshmen engineering and prospective engineering students-some of whom are still in high school-an opportunity to explore interesting and relevant topics of their choice. Five unique web-based lines of study, referred to as Elective Units, are being designed to capture the interests of students with diverse backgrounds and to encourage higher-level thinking. The goals of the project are to increase the commitment of freshman engineering students to the pursuit of engineering as an academic major and a profession, to enhance the interest of high school students in engineering, and to increase the number of women and underrepresented minorities matriculating into engineering and ultimately graduating with a degree in engineering. © 2012 American Society for Engineering Education.
• Oakes, W. C., Dexter, P., Hunter, J., Baygents, J. C., & Thompson, M. G. (2012). Early engineering through service-learning: Adapting a university model to high school. ASEE Annual Conference and Exposition, Conference Proceedings.
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  Abstract: The challenges of this next century require a new generation of engineering talent. In the United States, interest in engineering has remained flat and many groups within remain underrepresented relative to the overall population, specifically women and ethnic minorities. Attracting the next generation of diverse engineers requires a diverse set of pre-college experiences to connect diverse pathways leading to an engineering degree. One exciting approach is the use of service-learning to expose students to design and engineering. Servicelearning has been well established in many disciplines with positive impacts on interest, motivation, student satisfaction, personal success, desire, and retention of students who participated in service-learning projects. Service-learning is pedagogically consistent with literature on the recruitment and retention of women and other underrepresented groups in science and engineering. These benefits have been studied at the higher education level and show promise for pre-college as well. Service-learning connected to engineering also has an enormous potential for capitalizing on the wave of interest in community engagement among teenagers nationally. Connecting service to our community with engineering aligns perfectly with the National Academy's Changing the Conversation. This paper describes the adaptation of a successful university model to high school having been disseminated to more than 50 schools in 10 states. This paper highlights high school programs that have been integrated into the school day and are supported by a large Midwestern university and two large Southwestern universities. Example projects are described as well as the academic structure and teacher training processes. Demographic data shows that the model is attracting more female students and students from groups traditionally underrepresented in engineering. Data also shows that students are becoming more interested in engineering as a result of their experience in the service-learning programs. © 2012 American Society for Engineering Education.
• Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Wang, L., Zheng, X., & Zohar, Y. (2011). Adhesion dynamics of circulating tumor cells under shear flow in a bio-functionalized microchannel. Journal of Micromechanics and Microengineering, 21(5), 054033. doi:10.1088/0960-1317/21/5/054033
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  The adhesion dynamics of circulating tumor cells in a bio-functionalized microchannel under hydrodynamic loading is explored experimentally and analyzed theoretically. EpCAM antibodies are immobilized on the microchannel surface to specifically capture EpCAM-expressing target breast cancer cells MDA-MB-231 from a homogeneous cell suspension in shear flow. In the cross-stream direction, gravity is the dominant physical mechanism resulting in continuous interaction between the EpCAM cell receptors and the immobilized surface anti-EpCAM ligands. Depending on the applied shear rate, three dynamic states have been characterized: firm adhesion, rolling adhesion and free rolling. The steady-state velocity under adhesion- and free-rolling conditions as well as the time-dependent velocity in firm adhesion has been characterized experimentally, based on video recordings of target cell motion in functionalized microchannels. A previously reported theoretical model, utilizing a linear spring to represent the specific receptor–ligand bonds, has been adopted to analyze adhesion dynamics including features such as the cell–surface binding force and separation gap. By fitting theoretical predictions to experimental measurements, a unified exponential decay function is proposed to describe the target cell velocity evolution during capture; the fitting parameters, velocity and time scales, depend on the particular cell–surface system.
• Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Wang, L., Zheng, X., & Zohar, Y. (2010). Kinematics of Specifically Captured Circulating Tumor Cells in Bio-Functionalized Microchannels. IEEE\/ASME Journal of Microelectromechanical Systems, 19(4), 752-763. doi:10.1109/jmems.2010.2052021
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  The attachment kinematics of cancer cells under hydrodynamic loading in antibody-functionalized microchannels has been studied. Epithelial-cell-adhesion-molecule antibodies are immobilized on the microchannel surface for specific capture of the target cancer cells from homogeneous cell suspensions. The specific interaction between the cancer cell receptors and the immobilized antibodies under static conditions is demonstrated. The capture efficiency of the target cells from homogeneous suspensions under applied hydrodynamic flow field has been investigated, revealing a characteristic shear stress. Applying a lower stress allows the capture of most target cells, while the capture efficiency drops sharply with an increasing shear stress. The captured cells are spatially distributed along the microchannel; both the velocity and the distance travelled by cells prior to capture are measured. The characteristic time and length scales for cell capture are determined, and a log-normal statistical distribution is proposed to describe the observations. Furthermore, a first-order kinetic model for receptor-ligand bond formation provides a rough estimate of the cell adhesion rate constant. Under a low shear stress, the on-rate is much higher than the off-rate, allowing capture of most loaded cells. The off-rate constant increases exponentially with an increasing shear stress, such that above the characteristic stress level, most loaded cells avoid capture.
• Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Stopa, A., Zheng, X., & Zohar, Y. (2009). Detachment of captured cancer cells under flow acceleration in a bio-functionalized microchannel.. Lab on a chip, 9(12), 1721-31. doi:10.1039/b822172c
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  Attachment, deformation and detachment of N-cadherin expressing prostate and breast cancer cell lines in a functionalized microchannel under hydrodynamic loading have been studied. N-cadherin antibodies are immobilized on the microchannel surface to capture the target cancer cells, PC3N and MDA-MB-231-N, from a homogeneous cell suspension. Although difficult, a significant fraction of moving cells can be captured under a low flow rate. More than 90% of the target cells are captured after a certain incubation time under no flow condition. The mechanical response of a captured cancer cell to hydrodynamic flow field is investigated and, in particular, the effect of flow acceleration is examined. The observed cell deformation is dramatic under low acceleration, but is negligible under high acceleration. Consequently, the detachment of captured cells depends on both flow rate and flow acceleration. The flow rate required for cell detachment is a random variable that can be described by a log-normal distribution. Two flow acceleration limits have been identified for proper scaling of the flow rate required to detach captured cells. A time constant for the mechanical response of a captured cell, on the order of 1 min, has been identified for scaling the flow acceleration. Based on these acceleration limits and time constant, an exponential-like empirical model is proposed to predict the flow rate required for cell detachment as a function of flow acceleration.
• Baygents, J. C., Davis, J. R., Farrell, J., Gu, Z., Liao, Z., & Schulz, M. (2009). Estimating Dosing Rates and Energy Consumption for Electrocoagulation Using Iron and Aluminum Electrodes. Industrial & Engineering Chemistry Research, 48(6), 3112-3117. doi:10.1021/ie801086c
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  The effect of current density on dosing rates and energy requirements for iron and aluminum electrodes in a bench-scale electrocoagulation (EC) reactor have been investigated. Dissolution rates of the iron and aluminum anodes were independent of bulk solution pH values. Iron dosing rates followed Faraday’s law, but aluminum dosing rates averaged 83% greater than those predicted by Faraday’s law. Chemical corrosion of both the anode and cathode contributed to the extra-faradaic aluminum dosing. A method was developed to determine the faradaic power consumption as a function of the current density. An equation describing power dissipation by ohmic and faradaic mechanisms was derived and used to estimate energy consumption per unit coagulant dose for EC reactors operating over a wide range of conditions. The derived equation can be used to compare the operational costs for EC with those using chemical additives, such as alum or ferric chloride.
• Baygents, J. C., Davis, J. R., Farrell, J., Gu, Z., Liao, Z., & Schulz, M. C. (2009). Treatment of cooling tower blowdown water containing silica, calcium and magnesium by electrocoagulation.. Water science and technology : a journal of the International Association on Water Pollution Research, 60(9), 2345-52. doi:10.2166/wst.2009.675
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  This research investigated the effectiveness of electrocoagulation using iron and aluminium electrodes for treating cooling tower blowdown (CTB) waters containing dissolved silica (Si(OH)(4)), Ca(2 + ) and Mg(2 + ). The removal of each target species was measured as a function of the coagulant dose in simulated CTB waters with initial pH values of 5, 7, and 9. Experiments were also performed to investigate the effect of antiscaling compounds and coagulation aids on hardness ion removal. Both iron and aluminum electrodes were effective at removing dissolved silica. For coagulant doses < or =3 mM, silica removal was a linear function of the coagulant dose, with 0.4 to 0.5 moles of silica removed per mole of iron or aluminium. Iron electrodes were only 30% as effective at removing Ca(2 + ) and Mg(2 + ) as compared to silica. There was no measurable removal of hardness ions by aluminium electrodes in the absence of organic additives. Phosphonate based antiscaling compounds were uniformly effective at increasing the removal of Ca(2 + ) and Mg(2 + ) by both iron and aluminium electrodes. Cationic and amphoteric polymers used as coagulation aids were also effective at increasing hardness ion removal.
• Baygents, J. C., Farrell, J., & Schulz, M. C. (2009). Laboratory and pilot testing of electrocoagulation for removing scale-forming species from industrial process waters. International Journal of Environmental Science and Technology, 6(4), 521-526. doi:10.1007/bf03326091
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  This study investigated the performance of electrocoagulation using iron and aluminum electrodes for removing silica, calcium and magnesium from cooling tower blowdown and reverse osmosis reject waters. Experiments were conducted at both the bench and pilot scales to determine the levels of target species removal as a function of the coagulant dose. At the bench scale, aluminum removed the target compounds from both cooling tower blowdown and reverse osmosis reject more efficiently than iron. A 2 mM aluminum dose removed 80 % of the silica and 20 to 40 % of the calcium and magnesium. The same iron dose removed only 60 % of the silica and 10 to 20 % of the calcium and magnesium. When operated with iron electrodes, pilot unit performance was comparable to that of the bench unit, which suggests that such systems can be scaled-up on the basis of coagulant dose. However, when operated with aluminum electrodes the pilot unit underperformed the bench unit due to fouling of the electrode surfaces after a few hours of operation. This result was completely unexpected based on the short-term experiments performed using the bench unit.
• Safier, P. A., & Baygents, J. C. (2009). Electrohydrodynamic deformation of a miscible fluid stream by a transverse electric field. Langmuir, 25(10), 6000-6004.
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  PMID: 19374452;Abstract: Electrohydrodynamic deformation of a cylindrical fluid stream is analyzed with a quasi-electroneutral model. The stream is miscible with the surrounding liquid, though of different electrical conductivity and permittivity, and is subject to an electric field that acts transverse to the axis of the cylinder. The formulation allows for natural gradients of electrical conductivity and dielectric constant in the transition region between the stream and the surrounding liquid; these property variations are fully coupled to the fluid motion and are assumed to stem from concentration gradients of charge-carrying solutes. Dielectric and Coulombic body forces attendant to the time-dependent, spatial nonuniformities are accounted for. The strength of the electrically driven flows is such that transport of solutes is dominated by advection. As a consequence, the initial conductivity and dielectric constant differences, between the interior of the stream and the surrounding liquid, persist through significant deformation of the stream and characterize the rate at which the stream (continuously) deforms. Calculations for aqueous systems dominated by conductivity effects agree with measurements of stream deformation made by Rhodes et al. [J. Colloid Interface Sci. 1989, 129, 78]. Calculations for systems controlled by dielectric effects show that relative permittivity differences must be at least O(1) if noticeable deformations are to occur in a matter of seconds, which may explain why Trau et al. [Langmuir 1995,11,4665] discerned no deformations controlled by dielectric effects in low permittivity, low conductivity systems. An implication of these latter predictions is that experiments to isolate the role of dielectric constant mismatch may not be practicable. © 2009 American Chemical Society.
• Safier, P. A., & Baygents, J. C. (2009). Electrohydrodynamic deformation of a miscible fluid stream by a transverse electric field. Langmuir, 25(Issue 10). doi:10.1021/la802141u
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  Electrohydrodynamic deformation of a cylindrical fluid stream is analyzed with a quasi-electroneutral model. The stream is miscible with the surrounding liquid, though of different electrical conductivity and permittivity, and is subject to an electric field that acts transverse to the axis of the cylinder. The formulation allows for natural gradients of electrical conductivity and dielectric constant in the transition region between the stream and the surrounding liquid; these property variations are fully coupled to the fluid motion and are assumed to stem from concentration gradients of charge-carrying solutes. Dielectric and Coulombic body forces attendant to the time-dependent, spatial nonuniformities are accounted for. The strength of the electrically driven flows is such that transport of solutes is dominated by advection. As a consequence, the initial conductivity and dielectric constant differences, between the interior of the stream and the surrounding liquid, persist through significant deformation of the stream and characterize the rate at which the stream (continuously) deforms. Calculations for aqueous systems dominated by conductivity effects agree with measurements of stream deformation made by Rhodes et al. [J. Colloid Interface Sci. 1989, 129, 78]. Calculations for systems controlled by dielectric effects show that relative permittivity differences must be at least O(1) if noticeable deformations are to occur in a matter of seconds, which may explain why Trau et al. [Langmuir 1995,11,4665] discerned no deformations controlled by dielectric effects in low permittivity, low conductivity systems. An implication of these latter predictions is that experiments to isolate the role of dielectric constant mismatch may not be practicable. © 2009 American Chemical Society.
• Sounart, T. L., & Baygents, J. C. (2007). Lubrication theory for electro-osmotic flow in a non-uniform electrolyte. Journal of Fluid Mechanics, 576(Issue). doi:10.1017/s0022112006003867
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  A lubrication theory has been developed for the electro-osmotic flow of non-uniform buffers in narrow rectilinear channels. The analysis applies to systems in which the transverse dimensions of the channel are large compared with the Debye screening length of the electrolyte. In contrast with related theories of electrokinetic lubrication, here the streamwise variations of the velocity field stem from, and are nonlinearly coupled to, spatiotemporal variations in the electrolyte composition. Spatially nonuniform buffers are commonly employed in electrophoretic separation and transport schemes, including iso-electric focusing (IEF), isotachophoresis (ITP), field-amplified sample stacking (FASS), and high-ionic-strength electro-osmotic pumping. The fluid dynamics of these systems is controlled by a complex nonlinear coupling to the ion transport, driven by an applied electric field. Electrical conductivity gradients, attendent to the buffer non-uniformities, result in a variable electro-osmotic slip velocity and, in electric fields approaching 1 kV cm-1, Maxwell stresses drive the electrohydrodynamic circulation. Explicit semi-analytic expressions are derived for the fluid velocity, stream function, and electric field. The resulting approximations are found to be in good agreement with full numerical solutions for a prototype buffer, over a range of conditions typical of microfluidic systems. The approximations greatly simplify the computational analysis, reduce computation times by a factor 4-5, and, for the first time, provide general insight on the dominant fluid physics of two-dimensional electrically driven transport. © 2007 Cambridge University Press.
• Sounart, T. L., & Baygents, J. C. (2007). Lubrication theory for electro-osmotic flow in a non-uniform electrolyte. Journal of Fluid Mechanics, 576, 139-172.
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  Abstract: A lubrication theory has been developed for the electro-osmotic flow of non-uniform buffers in narrow rectilinear channels. The analysis applies to systems in which the transverse dimensions of the channel are large compared with the Debye screening length of the electrolyte. In contrast with related theories of electrokinetic lubrication, here the streamwise variations of the velocity field stem from, and are nonlinearly coupled to, spatiotemporal variations in the electrolyte composition. Spatially nonuniform buffers are commonly employed in electrophoretic separation and transport schemes, including iso-electric focusing (IEF), isotachophoresis (ITP), field-amplified sample stacking (FASS), and high-ionic-strength electro-osmotic pumping. The fluid dynamics of these systems is controlled by a complex nonlinear coupling to the ion transport, driven by an applied electric field. Electrical conductivity gradients, attendent to the buffer non-uniformities, result in a variable electro-osmotic slip velocity and, in electric fields approaching 1 kV cm-1, Maxwell stresses drive the electrohydrodynamic circulation. Explicit semi-analytic expressions are derived for the fluid velocity, stream function, and electric field. The resulting approximations are found to be in good agreement with full numerical solutions for a prototype buffer, over a range of conditions typical of microfluidic systems. The approximations greatly simplify the computational analysis, reduce computation times by a factor 4-5, and, for the first time, provide general insight on the dominant fluid physics of two-dimensional electrically driven transport. © 2007 Cambridge University Press.
• Baygents, J. C., Guzman, R., Heimark, R. L., Lee, L. M., & Zohar, Y. (2006). Low melting point agarose as a protection layer in photolithographic patterning of aligned binary proteins.. Lab on a chip, 6(8), 1080-5. doi:10.1039/b603095e
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  A novel photolithography method to build aligned patterns of two different proteins is presented. Chessboard patterns of 125 microm x 125 microm squares are constructed on a silicon dioxide substrate, using standard photoresist chemistries in combination with low-temperature oxygen plasma etching. Low-melting-point agarose (LMPA) is used to protect underlying protein layers and, at the appropriate stage, the digestive enzyme GELase (EPICENTRE) is used to selectively remove the prophylactic LMPA layers. Two antibodies, mouse-IgG and human-IgG, were immobilized and patterned by this procedure. The patterned antibodies maintained the specificity of their antigen-antibody binding, as demonstrated by fluorescence microscopy. In addition, normalized fluorescence intensity profiles illustrate that the patterned proteins layers are uniform (standard deviations below 0.05). Finally, a trypsin activity test was conducted to probe the effect of the patterning protocol on immobilized enzymes; the results imply that this photolithographic process using LMPA as a protection layer preserves 70% of immobilized enzyme activity.
• Baygents, J. C., Heimark, R. L., Lee, L. M., & Zohar, Y. (2006). Self-aligned immobilization of proteins utilizing PEG patterns.. Nanotechnology, 17(4), S29-33. doi:10.1088/0957-4484/17/4/006
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  A novel self-aligned method to selectively immobilize proteins on a silicon dioxide surface is developed in conjunction with a standard lift-off patterning technique of a PEG layer. The approach is designed to photolithographically pattern regions that specifically bind target proteins and particles, surrounded by regions that suppress non-specific attachment of bio-species. The physical and biological properties of the derivatized surfaces at the end of the fabrication process are characterized.
• Short, M. B., Baygents, J. C., & Goldstein, R. E. (2006). A free-boundary theory for the shape of the ideal dripping icicle. Physics of Fluids, 18(8).
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  Abstract: The growth of icicles is considered as a free-boundary problem. A synthesis of atmospheric heat transfer, geometrical considerations, and thin-film fluid dynamics leads to a nonlinear ordinary differential equation for the shape of a uniformly advancing icicle, the solution to which defines a parameter-free shape which compares very favorably with that of natural icicles. Away from the tip, the solution has a power-law form identical to that recently found for the growth of stalactites by precipitation of calcium carbonate. This analysis thereby explains why stalactites and icicles are so similar in form despite the vastly different physics and chemistry of their formation. In addition, a curious link is noted between the shape so calculated and that found through consideration of only the thin coating water layer. © 2006 American Institute of Physics.
• Short, M. B., Baygents, J. C., & Goldstein, R. E. (2006). A free-boundary theory for the shape of the ideal dripping icicle. Physics of Fluids, 18(Issue 8). doi:10.1063/1.2335152
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  The growth of icicles is considered as a free-boundary problem. A synthesis of atmospheric heat transfer, geometrical considerations, and thin-film fluid dynamics leads to a nonlinear ordinary differential equation for the shape of a uniformly advancing icicle, the solution to which defines a parameter-free shape which compares very favorably with that of natural icicles. Away from the tip, the solution has a power-law form identical to that recently found for the growth of stalactites by precipitation of calcium carbonate. This analysis thereby explains why stalactites and icicles are so similar in form despite the vastly different physics and chemistry of their formation. In addition, a curious link is noted between the shape so calculated and that found through consideration of only the thin coating water layer. © 2006 American Institute of Physics.
• Beck, W., Baygents, J. C., Beck, W. F., Goldstein, R. E., Short, M. B., Stone, D., & Toomey, R. S. (2005). The Platonic Ideal of Stalactite Growth. Bulletin of the American Physical Society, 57.
• Short, M. B., Baygents, J. C., & Goldstein, R. E. (2005). Stalactite growth as a free-boundary problem. AIChE Annual Meeting, Conference Proceedings, 439-.
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  Abstract: The astonishing variety and beauty of structures found in limestone caves, from stalactites and stalagmites to soda straws, draperies, and helictites, have been the subject of human wonder for hundreds if not thousands of years. There is little debate about the fundamental chemical processes responsible for their development. Water enters the cave from the overlying environment with significant concentrations of dissolved carbon dioxide and calcium. As the partial pressure of carbon dioxide in the cave is lower than that in the overlying rock, carbon dioxide outgases from the water. This raises the pH and leads to supersaturation and then precipitation of calcium carbonate. Yet, this chemical picture is only part of the story, for it does not in any direct way answer the most obvious morphological question: Why are stalactites long and slender, often roughly conical (resembling icicles)? While some studies address the dynamics of speleothem morphology, none quantitatively explains this most basic fact. In the work to be presented, we show that the combination of thin film fluid dynamics, calcium carbonate chemistry, and carbon dioxide diffusion and outgassing leads to a local geometric growth law for the surface evolution that quantitatively explains the shapes of natural stalactites. Here we provide details of this free-boundary calculation, exploiting a strong separation of time scales between that for diffusion within the layer, the time during which a fluid parcel is in contact with the growing surface, and the time scale of growth. When the flow rate, the scale of the stalactite, and the chemistry are in the ranges typically found in nature, the local growth rate is proportional to the local thickness of the fluid layer, itself determined by Stokes flow over the surface. Analytical and numerical studies of this law establish that a broad class of initial conditions is attracted to an ideal universal shape. Found under a set of limiting assumptions, this may be thought of as the Platonic ideal of speleothem growth. While real stalactites have more complex shapes due to instabilities and cave inhomogeneities, statistical analysis of stalactite shapes from Kartchner Caverns (Benson, AZ) yields excellent agreement between the average shape of natural stalactites and the ideal shape. This work serves to emphasize a broad class of problems that demands considerable attention-free-boundary dynamics in precipitative pattern formation. Beyond speleothems, these include structures as diverse as hydrothermal vents, chemical gardens, mollusc shells, and tubes whose growth is templated by bubbles.
• Short, M. B., Baygents, J. C., & Goldstein, R. E. (2005). Stalactite growth as a free-boundary problem. Physics of Fluids, 17(8), 1-12.
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  Abstract: Stalactites, the most familiar structures found hanging from the ceilings of limestone caves, grow by the precipitation of calcium carbonate from within a thin film of fluid flowing down their surfaces. We have recently shown [M. B. Short, J. C. Baygents, J. W. Beck, D. A. Stone, R. S. Toomey III, and R. E. Goldstein, "Stalactite growth as a free-boundary problem: A geometric law and its Platonic ideal," Phys. Rev. Lett. 94, 018501 (2005)] that the combination of thin-film fluid dynamics, calcium carbonate chemistry, and carbon dioxide diffusion and outgassing leads to a local geometric growth law for the surface evolution which quantitatively explains the shapes of natural stalactites. Here we provide details of this free-boundary calculation, exploiting a strong separation of time scales among that for diffusion within the layer, contact of a fluid parcel with the growing surface, and growth. When the flow rate, the scale of the stalactite, and the chemistry are in the ranges typically found in nature, the local growth rate is proportional to the local thickness of the fluid layer, itself determined by Stokes flow over the surface. Numerical studies of this law establish that a broad class of initial conditions is attracted to an ideal universal shape, whose mathematical form is found analytically. Statistical analysis of stalactite shapes from Kartchner Caverns (Benson, AZ) shows excellent agreement between the average shape of natural stalactites and the ideal shape. Generalizations of these results to nonaxisymmetric speleothems are discussed. © 2005 American Institute of Physics.
• Short, M. B., Baygents, J. C., & Goldstein, R. E. (2005). Stalactite growth as a free-boundary problem. Physics of Fluids, 17(Issue 8). doi:10.1063/1.2006027
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  Stalactites, the most familiar structures found hanging from the ceilings of limestone caves, grow by the precipitation of calcium carbonate from within a thin film of fluid flowing down their surfaces. We have recently shown [M. B. Short, J. C. Baygents, J. W. Beck, D. A. Stone, R. S. Toomey III, and R. E. Goldstein, "Stalactite growth as a free-boundary problem: A geometric law and its Platonic ideal," Phys. Rev. Lett. 94, 018501 (2005)] that the combination of thin-film fluid dynamics, calcium carbonate chemistry, and carbon dioxide diffusion and outgassing leads to a local geometric growth law for the surface evolution which quantitatively explains the shapes of natural stalactites. Here we provide details of this free-boundary calculation, exploiting a strong separation of time scales among that for diffusion within the layer, contact of a fluid parcel with the growing surface, and growth. When the flow rate, the scale of the stalactite, and the chemistry are in the ranges typically found in nature, the local growth rate is proportional to the local thickness of the fluid layer, itself determined by Stokes flow over the surface. Numerical studies of this law establish that a broad class of initial conditions is attracted to an ideal universal shape, whose mathematical form is found analytically. Statistical analysis of stalactite shapes from Kartchner Caverns (Benson, AZ) shows excellent agreement between the average shape of natural stalactites and the ideal shape. Generalizations of these results to nonaxisymmetric speleothems are discussed. © 2005 American Institute of Physics.
• Short, M. B., Baygents, J. C., Beck, J. W., Stone, D. A., S., R., & Goldstein, R. E. (2005). Stalactite growth as a free-boundary problem: A geometric law and its platonic ideal. Physical Review Letters, 94(1).
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  Abstract: The chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we consider the interplay of thin-film fluid dynamics, calcium carbonate chemistry, and CO2 transport in the cave to show that stalactites evolve according to a novel local geometric growth law which exhibits extreme amplification at the tip as a consequence of the locally-varying fluid layer thickness. Studies of this model show that a broad class of initial conditions is attracted to an ideal shape which is strikingly close to a statistical average of natural stalactites. © 2005 The American Physical Society.
• Short, M. B., Baygents, J. C., Beck, J. W., Stone, D. A., Toomey, R. S., & Goldstein, R. E. (2005). Stalactite growth as a free-boundary problem: A geometric law and its platonic ideal. Physical Review Letters, 94(Issue 1). doi:10.1103/physrevlett.94.018501
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  The chemical mechanisms underlying the growth of cave formations such as stalactites are well known, yet no theory has yet been proposed which successfully accounts for the dynamic evolution of their shapes. Here we consider the interplay of thin-film fluid dynamics, calcium carbonate chemistry, and CO2 transport in the cave to show that stalactites evolve according to a novel local geometric growth law which exhibits extreme amplification at the tip as a consequence of the locally-varying fluid layer thickness. Studies of this model show that a broad class of initial conditions is attracted to an ideal shape which is strikingly close to a statistical average of natural stalactites. © 2005 The American Physical Society.
• Sounart, T. L., Safier, P. A., & Baygents, J. C. (2005). Theory and simulation of isoelectric focusing. Separation Science and Technology, 7(C), 41-68.
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  Abstract: IEF is an electrophoretic process that hinges on the mobility versus pH behavior of ampholytes. The basic theory of IEF tells us that separands focus about their pI in a Gaussian distribution. Peak height and variance depend on the competition between diffusion away from the pI and electromigration towards it. Comprehensive simulations of IEF involve the numerical solution to conservation laws for all the relevant amphoteric and ionogenic species in the separations milieu. The conservation relations are non-linearly coupled to the driving electric field and through the complicated mass-action relations. With the increased speed of microprocessors, one-dimensional simulations of the type shown here are now readily managed. The simulations offer the possibility of gaining insight into the detailed dynamics of the unfolding separations process. To see a more comprehensive exposition of IEF simulation results, particularly with regard to pH gradient development, the reader should refer the monograph by Mosher et al. © 2005 Elsevier Inc.
• Stone, D. A., Lewellyn, B., Baygents, J. C., & Goldstein, R. E. (2005). Precipitative growth templated by a fluid jet. Langmuir, 21(24), 10916-10919.
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  PMID: 16285753;Abstract: Tubular growth by chemical precipitation at the interface between two fluids, a jet and its surroundings, underlies the development of such important structures as chimneys at hydrothermal vents. This growth is associated with strong thermal and/or solute gradients localized at those interfaces, and these gradients, in turn, often produce radial compositional stratification of the resulting tube wall. A fundamental question underlying these processes is how the interplay between diffusion, advection, and precipitation determines the elongation rate of the tubes. Here we report experimental and theoretical results that reveal a regime in which there exists a new scaling law for tube growth. The model system studied consists of a jet of aqueous ammonia injected into a ferrous sulfate solution, precipitating iron hydroxides with varying oxidation states at the jet boundary. Despite the complex chemistry and dynamics underlying the precipitation, the tube growth exhibits a strikingly simple scaling form, with characteristic lengths and times increasing linearly with the mean velocity of the jet. These observations follow from a kinetic model of advection-dominated flows. © 2005 American Chemical Society.
• Stone, D. A., Lewellyn, B., Baygents, J. C., & Goldstein, R. E. (2005). Precipitative growth templated by a fluid jet. Langmuir, 21(Issue 24). doi:10.1021/la052064z
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  Tubular growth by chemical precipitation at the interface between two fluids, a jet and its surroundings, underlies the development of such important structures as chimneys at hydrothermal vents. This growth is associated with strong thermal and/or solute gradients localized at those interfaces, and these gradients, in turn, often produce radial compositional stratification of the resulting tube wall. A fundamental question underlying these processes is how the interplay between diffusion, advection, and precipitation determines the elongation rate of the tubes. Here we report experimental and theoretical results that reveal a regime in which there exists a new scaling law for tube growth. The model system studied consists of a jet of aqueous ammonia injected into a ferrous sulfate solution, precipitating iron hydroxides with varying oxidation states at the jet boundary. Despite the complex chemistry and dynamics underlying the precipitation, the tube growth exhibits a strikingly simple scaling form, with characteristic lengths and times increasing linearly with the mean velocity of the jet. These observations follow from a kinetic model of advection-dominated flows. © 2005 American Chemical Society.
• Sounart, T. L., & Baygents, J. C. (2001). Electrically-driven fluid motion in channels with streamwise gradients of the electrical conductivity. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 195(1-3), 59-75.
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  Abstract: Electroosmotic motion through charged, narrow-bore channels and capillaries is analyzed for the case where there are dominantly-axial gradients in the composition of the flowing electrolyte. The channel width is assumed to be large compared with the Debye screening length, and the electroosmotic slip velocity along the channel wall is taken to vary locally with the ionic strength, pH and electric field. Owing to the wall slip condition, the velocity distribution is nonlinearly coupled to the composition variations within the fluid. The prototype problem studied is one in which buffer ions and other solutes (e.g. analytes) are initially distributed in a sample zone that is sandwiched between uniform running buffer. For the situations considered, the conductivity of the sample zone differs significantly from that of the running buffer; such configurations are common to stacking and electroosmotic pumping protocols. In a frame of reference that moves with the mean velocity of the flow, the velocity field exhibits flow separation in the neighborhood of the conductivity variations and this gives rise to solutal mixing and dispersion in and about the sample zone. Copyright © 2001 Elsevier Science B.V.
• Sounart, T. L., & Baygents, J. C. (2000). Simulation of electrophoretic separations by the flux-corrected transport method. Journal of Chromatography A, 890(2), 321-336.
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  PMID: 11009036;Abstract: Electrophoretic separations at typical experimental electric field strengths have been simulated by applying the flux-corrected transport (FCT) finite difference method to the transient, one-dimensional electrophoresis model. The performance of FCT on simulations of zone electrophoresis (ZE), isotachophoresis (ITP), and isoelectric focusing (IEF) has been evaluated. An FCT algorithm, with a three-point, central spatial discretization, yields numerical solutions without numerical oscillations or spurious peaks, which have plagued previously-published second-order solutions to benchmark ZE and ITP problems. Moreover, the FCT technique captures sharp zone boundaries and IEF peaks more accurately than previously-published, first-order upwind schemes. (C) 2000 Elsevier Science B.V.
• Sounart, T. L., & Baygents, J. C. (2000). Simulation of electrophoretic separations by the flux-corrected transport method. Journal of Chromatography A, 890(Issue 2). doi:10.1016/s0021-9673(00)00500-8
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  Electrophoretic separations at typical experimental electric field strengths have been simulated by applying the flux-corrected transport (FCT) finite difference method to the transient, one-dimensional electrophoresis model. The performance of FCT on simulations of zone electrophoresis (ZE), isotachophoresis (ITP), and isoelectric focusing (IEF) has been evaluated. An FCT algorithm, with a three-point, central spatial discretization, yields numerical solutions without numerical oscillations or spurious peaks, which have plagued previously-published second-order solutions to benchmark ZE and ITP problems. Moreover, the FCT technique captures sharp zone boundaries and IEF peaks more accurately than previously-published, first-order upwind schemes. (C) 2000 Elsevier Science B.V.
• Sounart, T. L., & Baygents, J. C. (2000). Simulation of electrophoretic separations: Effect of numerical and molecular diffusion on pH calculations in poorly buffered systems. Electrophoresis, 21(12), 2287-2295.
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  PMID: 10939437;Abstract: A poorly buffered cationic isotachophoresis separation, first simulated by Reijenga and Kasica, has been revisited to demonstrate that an inconsistent description of solute and charge transport can lead to significant errors in the pH calculation. The separation is first simulated using a second-order finite difference scheme to show that omission of molecular diffusion from the charge balance results in a pH profile with spurious dips in the steady-state zone boundaries. The separation is also simulated using two first order methods that employ numerical diffusion to stabilize solutions against spatiotemporal oscillations. Similar pH dips are generated by these first-order schemes, even when molecular diffusion is included in the charge balance, if numerical diffusion is not considered amongst the charge transport mechanisms. When numerical diffusion, inherent in the discretization of the component balances, is introduced to the charge balance, the spurious pH dips are eliminated. The results indicate that (i) pH dips originally reported by Reijenga and Kasicka are merely artifacts of their numerical model, and (ii) nonoscillatory numerical techniques, such as upwinding and flux limiters, should incorporate artificial transport mechanisms in the charge as well as the solute balances.
• Sounart, T. L., & Baygents, J. C. (2000). Simulation of electrophoretic separations: Effect of numerical and molecular diffusion on pH calculations in poorly buffered systems. Electrophoresis, 21(Issue 12). doi:10.1002/1522-2683(20000701)21:12<2095::aid-elps2287>3.0.co;2-y
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  A poorly buffered cationic isotachophoresis separation, first simulated by Reijenga and Kasica, has been revisited to demonstrate that an inconsistent description of solute and charge transport can lead to significant errors in the pH calculation. The separation is first simulated using a second-order finite difference scheme to show that omission of molecular diffusion from the charge balance results in a pH profile with spurious dips in the steady-state zone boundaries. The separation is also simulated using two first order methods that employ numerical diffusion to stabilize solutions against spatiotemporal oscillations. Similar pH dips are generated by these first-order schemes, even when molecular diffusion is included in the charge balance, if numerical diffusion is not considered amongst the charge transport mechanisms. When numerical diffusion, inherent in the discretization of the component balances, is introduced to the charge balance, the spurious pH dips are eliminated. The results indicate that (i) pH dips originally reported by Reijenga and Kasicka are merely artifacts of their numerical model, and (ii) nonoscillatory numerical techniques, such as upwinding and flux limiters, should incorporate artificial transport mechanisms in the charge as well as the solute balances.
• Baygents, J. C., Baygents, J. C., Bolster, C. H., Bolster, C. H., Camesano, T. A., Camesano, T. A., Desantis, A. A., Desantis, A. A., Hornberger, G. M., Hornberger, G. M., Logan, B. E., Logan, B. E., Mills, A. L., Mills, A. L., Unice, K. M., Unice, K. M., Wilson, J. L., & Wilson, J. L. (1999). COMMENT ON : A METHOD FOR CALCULATING BACTERIAL DEPOSITION COEFFICIENTS USING THE FRACTION OF BACTERIA RECOVERED FROM LABORATORY COLUMNS. Environmental Science & Technology, 33(8), 1316-1319. doi:10.1021/es9810235
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  ADVERTISEMENT RETURN TO ISSUEPREVCorrespondence/Rebut...Correspondence/RebuttalNEXTComment on “A Method for Calculating Bacterial Deposition Coefficients Using the Fraction of Bacteria Recovered from Laboratory Columns”Bruce E. Logan, Terri A. Camesano, Amanda A. DeSantis, Kenneth M. Unice, and James C. BaygentsView Author Information Department of Civil and Environmental Engineering The Pennsylvania State University University Park, Pennsylvania 16802 Department of Chemical and Environmental Engineering The University of Arizona Tucson, Arizona 85721Cite this: Environ. Sci. Technol. 1999, 33, 8, 1316–1317Publication Date (Web):March 9, 1999Publication History Published online9 March 1999Published inissue 1 April 1999https://doi.org/10.1021/es9810235Copyright © 1999 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views168Altmetric-Citations8LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (32 KB) Get e-AlertsSUBJECTS:Bacteria,Colloids,Deposition,Fluids,Soils Get e-Alerts
• Belongia, B. M., Haworth, P. D., Baygents, J. C., & Raghavan, S. (1999). Treatment of alumina and silica chemical mechanical polishing waste by electrodecantation and electrocoagulation. Journal of the Electrochemical Society, 146(Issue 11). doi:10.1149/1.1392602
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  Electrocoagulation and electrodecantation were investigated as methods to concentrate solids from the dilute suspensions typically encountered as waste streams of chemical mechanical polishing operations. Model silica and alumina suspension containing particles of approximately 200 nm in diameter were studied. 3 L batches of suspension were subjected to electric fields of several volts per centimeter and monitored for particle removal. Electrodecantation was shown to clarify charge stabilized, low conductivity suspensions (20 mS/cm) without modifying the mean particle size or surface-charge characteristics. The technique is thus suited to circumstances where recycle and reuse of particles is desirable, though the results also show that Joule heating may disrupt the decantation process and so must be controlled in order to apply the method to higher conductivity suspensions. Electrocoagulation was shown to effectively destabilize and clarify high conductivity suspensions (1300 μS/cm), producing aggregates several-fold larger than the primary particle size, which subsequently sedimented from suspension. Intermittent application of the electric field was found to yield superior rates of particle removal while consuming substantially less electrical power (ca. 1 Wh/L of clear solution).
• Logan, B. E., Camesano, T. A., DeSantis, A. A., Unice, K. M., Baygents, J. C., Bolster, C. H., Hornberger, G. M., Mills, A. L., & Wilson, J. L. (1999). Comment on 'a method for calculating bacterial deposition coefficients using the fraction of bacteria recovered from laboratory columns' [2] (multiple letters). Environmental Science and Technology, 33(8), 1316-1319.
• Albinger, O., Arnold, R. G., Baygents, J. C., Biesemeyer, B. K., Glynn, J. R., & Ogden, K. L. (1998). Variation of Surface Charge Density in Monoclonal Bacterial Populations: Implications for Transport through Porous Media. Environmental Science & Technology, 32(11), 1596-1603. doi:10.1021/es9707116
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  The forced convection of a monodisperse, monoclonal suspension of bacteria through a uniform, saturated porous medium has been investigated. Bench-scale column studies were carried out to measure the removal of microorganisms from suspension due to attachment to the surfaces of the solid phase. The columns were packed with 40-μm borosilicate glass beads, and bacterial sorption was measured as a function of depth in the column using a leucine radiolabel assay. The strains A1264 and CD1 were examined separately. Colloid filtration theory was used to interpret the data, and the average, or effective, affinity of the bacteria for the glass beads was found to decrease with distance traveled through the column. It is postulated that, under these circumstances, the cell/collector affinity (that is, the collision efficiency α) varied due to intrapopulational differences in bacterial surface characteristics. A simple bimodal probability density function, consisting of two Dirac delta functions, was found to satisf...
• Baygents, J. C., & Baldessari, F. (1998). Electrohydrodynamic instability in a thin fluid layer with an electrical conductivity gradient. Physics of Fluids, 10(1), 301-311.
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  Abstract: The onset of electrohydrodynamic motion associated with the imposition of an electric field across a thin layer of liquid has been investigated for the case in which the electrical conductivity varies linearly over the depth of the layer. The variation of the conductivity is due to concentration gradients in the charge-carrying solutes and its spatiotemporal evolution is represented by a convective-diffusion equation. When the viscous relaxation time is long compared to the time for charge relaxation, the analysis reveals that the neutral stability curves for the layer can be characterized by three dimensionless parameters: Rae≡d∈E02Δσ/μK effσ0, an electrical Rayleigh number; Δσ/σ0, the relative conductivity increment: and α, the transverse wave number of the disturbance. Here d is the thickness, ∈ is the dielectric constant, and μ is the viscosity of the layer, E0 is the applied field strength at the lower conductivity boundary, and Keff is an effective diffusivity associated with the Brownian motion of the charge-carrying solutes. With stress-free boundaries, at which the electrical conductivity and current are prescribed, the critical Rae is 1.416×104 at a critical transverse wave number of 1.90 when Δσ/σ0 is 8. As Δσ/σ0 increases, the critical Rae increases and shifts to slightly shorter wavelength disturbances; the critical imposed field strength, however, passes through a minimum because the lower-conductivity boundary exerts a considerable stabilizing influence in the presence of steep conductivity gradients. For Δσ/σ0 ≲8, the critical Rayleigh number increases as Δσ/σ0, decreases and the layer is only sensitive to long wavelength disturbances (α
• Baygents, J. C., & Baldessari, F. (1998). Electrohydrodynamic instability in a thin fluid layer with an electrical conductivity gradient. Physics of Fluids, 10(Issue 1). doi:10.1063/1.869567
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  The onset of electrohydrodynamic motion associated with the imposition of an electric field across a thin layer of liquid has been investigated for the case in which the electrical conductivity varies linearly over the depth of the layer. The variation of the conductivity is due to concentration gradients in the charge-carrying solutes and its spatiotemporal evolution is represented by a convective-diffusion equation. When the viscous relaxation time is long compared to the time for charge relaxation, the analysis reveals that the neutral stability curves for the layer can be characterized by three dimensionless parameters: Rae≡d∈E02Δσ/μK effσ0, an electrical Rayleigh number; Δσ/σ0, the relative conductivity increment: and α, the transverse wave number of the disturbance. Here d is the thickness, ∈ is the dielectric constant, and μ is the viscosity of the layer, E0 is the applied field strength at the lower conductivity boundary, and Keff is an effective diffusivity associated with the Brownian motion of the charge-carrying solutes. With stress-free boundaries, at which the electrical conductivity and current are prescribed, the critical Rae is 1.416×104 at a critical transverse wave number of 1.90 when Δσ/σ0 is 8. As Δσ/σ0 increases, the critical Rae increases and shifts to slightly shorter wavelength disturbances; the critical imposed field strength, however, passes through a minimum because the lower-conductivity boundary exerts a considerable stabilizing influence in the presence of steep conductivity gradients. For Δσ/σ0 ≲8, the critical Rayleigh number increases as Δσ/σ0, decreases and the layer is only sensitive to long wavelength disturbances (α
• Baygents, J. C., Rivette, N. J., & Stone, H. A. (1998). Electrohydrodynamic deformation and interaction of drop pairs. Journal of Fluid Mechanics, 368(Issue). doi:10.1017/s0022112098001797
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  The motion of two drops in a uniform electric field is considered using the leaky dielectric model. The drops are assumed to have no native charge and a dielectrophoretic effect favours translation of the drops toward one another. However circulatory flows that stem from electrohydrodynamic stresses may either act with or against this dielectrophoretic effect. Consequently, both prolate and oblate drop deformations may be generated and significant deformation occurs near drop contact owing to enhancement of the local electric field. For sufficiently widely spaced drops, electrohydrodynamic flows dominate direct electrical interactions so drops may be pushed apart, though closely spaced drops almost always move together as a result of the electrical interaction or deformation.
• Baygents, J. C., Rivette, N. J., & Stone, H. A. (1998). Electrohydrodynamic deformation and interaction of drop pairs. Journal of Fluid Mechanics, 368, 359-375.
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  Abstract: The motion of two drops in a uniform electric field is considered using the leaky dielectric model. The drops are assumed to have no native charge and a dielectrophoretic effect favours translation of the drops toward one another. However circulatory flows that stem from electrohydrodynamic stresses may either act with or against this dielectrophoretic effect. Consequently, both prolate and oblate drop deformations may be generated and significant deformation occurs near drop contact owing to enhancement of the local electric field. For sufficiently widely spaced drops, electrohydrodynamic flows dominate direct electrical interactions so drops may be pushed apart, though closely spaced drops almost always move together as a result of the electrical interaction or deformation.
• Glynn, J. R., Belongia, B. M., Arnold, R. G., Ogden, K. L., & Baygents, J. C. (1998). Capillary electrophoresis measurements of electrophoretic mobility for colloidal particles of biological interest. Applied and Environmental Microbiology, 64(Issue 7). doi:10.1128/aem.64.7.2572-2577.1998
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  The electrophoretic mobilities of three bacterial strains were investigated by capillary electrophoresis (CE) and were compared with results obtained by microelectrophoresis (ME). The CE measurements yielded bimodal electropherograms for two of the strains, thus illustrating for the first time that surface charge variations within a monoclonal population can be probed by CE. Intrapopulation variations were not detected by ME. The mobilities of three chemically distinct types of latex microspheres were also measured. Differences between the mean mobilities obtained by CE and ME were not statistically significant (P ≤ 0.50); the standard deviations of the CE measurements were typically 2 to 10 times smaller than those obtained by comparable ME measurements. The reproducibility of CE permitted batch-to- batch mobility variations to be probed for the bacteria (one of the strains exhibited such variations), and aggregation was evident in one of the latex suspensions. These effects were not measurable with ME.
• Baygents, J. C., Schwarz, B. C., Deshmukh, R. R., & Bier, M. (1997). Recycling electrophoretic separations: Modeling of isotachophoresis and isoelectric focusing. Journal of Chromatography A, 779(1-2), 165-183.
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  Abstract: The conventional, one-dimensional model that is the foundation for the dynamic simulation of electrophoretic separations is modified to describe the essential features of recycling electrophoresis instruments. Simulations are performed for the isoelectric focusing (IEF) and the isotachophoresis (ITP) modes. Results are compared with experimental data from prototype recycling free-flow IEF and ITP devices. Agreement between the experiments and the simulations is favorable, though electrode and electroosmotic effects, which are omitted from the model, are noticeable in the IEF instrument. Three parameters relevant to the design of recycling electrophoresis devices, viz. the number of ports for the recycle manifold, the residence time in the separation chamber per cycle, and the current density, are investigated with the model.
• Baygents, J. C., Schwarz, B. C., Deshmukh, R. R., & Bier, M. (1997). Recycling electrophoretic separations: Modeling of isotachophoresis and isoelectric focusing. Journal of Chromatography A, 779(Issue 1-2). doi:10.1016/s0021-9673(96)00963-6
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  The conventional, one-dimensional model that is the foundation for the dynamic simulation of electrophoretic separations is modified to describe the essential features of recycling electrophoresis instruments. Simulations are performed for the isoelectric focusing (IEF) and the isotachophoresis (ITP) modes. Results are compared with experimental data from prototype recycling free-flow IEF and ITP devices. Agreement between the experiments and the simulations is favorable, though electrode and electroosmotic effects, which are omitted from the model, are noticeable in the IEF instrument. Three parameters relevant to the design of recycling electrophoresis devices, viz. the number of ports for the recycle manifold, the residence time in the separation chamber per cycle, and the current density, are investigated with the model.
• Belongia, B. M., & Baygents, J. C. (1997). Measurements on the diffusion coefficient of colloidal particles by Taylor-Aris dispersion. Journal of Colloid and Interface Science, 195(1), 19-31.
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  Abstract: Taylor-Aris dispersion in narrow-bore capillaries is used to measure the diffusion coefficient of colloidal particles in aqueous suspension. The method is shown to yield accurate results for particles up to about 0.3 μm in diameter; the measurement time for larger particles is prohibitively long and impractical. For hydrophobic particles, interactions with the capillary walls can introduce error into the interpretation of the data. The measurements also suggest that buoyancy-driven particle motion can introduce error. Consequently, a method similar to capillary hydrodynamic fractionation was developed to establish when these factors were of negligible effect. The results constitute an order-and-a-half improvement in the sensitivity of the technique, which has been recently shown to work for nanometer-sized proteins. The data suggest that, when matched with the appropriate theory, dispersion in capillaries may be a useful probe of colloidal and gravitational interaction potentials.
• Belongia, B. M., & Baygents, J. C. (1997). Measurements on the diffusion coefficient of colloidal particles by Taylor-Aris dispersion. Journal of Colloid and Interface Science, 195(Issue 1). doi:10.1006/jcis.1997.5131
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  Taylor-Aris dispersion in narrow-bore capillaries is used to measure the diffusion coefficient of colloidal particles in aqueous suspension. The method is shown to yield accurate results for particles up to about 0.3 μm in diameter; the measurement time for larger particles is prohibitively long and impractical. For hydrophobic particles, interactions with the capillary walls can introduce error into the interpretation of the data. The measurements also suggest that buoyancy-driven particle motion can introduce error. Consequently, a method similar to capillary hydrodynamic fractionation was developed to establish when these factors were of negligible effect. The results constitute an order-and-a-half improvement in the sensitivity of the technique, which has been recently shown to work for nanometer-sized proteins. The data suggest that, when matched with the appropriate theory, dispersion in capillaries may be a useful probe of colloidal and gravitational interaction potentials.
• Erker, J. A., & Baygents, J. C. (1996). Electrohydrodynamic interaction of a pair of spherical drops. NASA Conference Publication, 731-736.
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  Abstract: The axisymmetric electrohydrodynamic interaction between two spherical emulsion drops has been examined, using the leaky dielectric model to represent the constitutive behavior of the liquid phases. The results follow from the general solutions in bispherical coordinates to the Laplace equation for the electric potential and the Stokes equations for the velocity field. For drops of similar composition, the electrical interactions induced between the drops by the imposition of the electric field are always attractive, meaning they favor coalescence of the drop pair. The hydrodynamic interactions, however, are not always favorable and, indeed, are shown in certain circumstances to drive the drops apart.
• Erker, J. A., & Baygents, J. C. (1996). The equilibrium electric potential and surface charge density of spherical emulsion drops with thin double layers. Journal of Colloid and Interface Science, 179(1), 76-88.
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  Abstract: Analytic approximations are derived for the solution to the Poisson-Boltzmann equation as applied to a spherical emulsion drop containing a binary electrolyte. Particular attention is given to the drop interior and the formulas that result are easily evaluated. The approximations are obtained by two separate asymptotic methods, which are analogous to those used previously by others to describe the electric potential profile on the exterior of a spherical colloidal particle. The analyses apply to emulsion drops with thin double layers, meaning the drop radius a is large compared to κ-1 and κ̄-1, the respective Debye screening lengths for the exterior and interior of the drop. Using δ = (aκ̄)-1 as a perturbation parameter, we obtain a matched-asymptotic solution that adds corrections through O(δ3) to the flat-plate and Debye-Huckel solutions of the Poisson-Boltzmann equation. In the process, we recover expressions for the drop exterior that constitute an O(δ) improvement over the previously published results. Through a nonlinear transformation of the independent variable, we also derive a uniformly valid approximation that iteratively adds a correction to the flat-plate problem. Each technique yields accurate solutions. For example, the maximum relative error over the drop interior is on the order of 1% for aκ as low as 5 with surface potentials as high as 250 mV. Accuracy improves for larger values of aκ̄, with a maximum relative error below 0.1% for aκ̄ > 15. The asymptotic techniques are also used to obtain expressions for the surface charge density, with equally satisfactory results.
• Erker, J. A., & Baygents, J. C. (1996). The equilibrium electric potential and surface charge density of spherical emulsion drops with thin double layers. Journal of Colloid and Interface Science, 179(Issue 1). doi:10.1006/jcis.1996.0190
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  Analytic approximations are derived for the solution to the Poisson-Boltzmann equation as applied to a spherical emulsion drop containing a binary electrolyte. Particular attention is given to the drop interior and the formulas that result are easily evaluated. The approximations are obtained by two separate asymptotic methods, which are analogous to those used previously by others to describe the electric potential profile on the exterior of a spherical colloidal particle. The analyses apply to emulsion drops with thin double layers, meaning the drop radius a is large compared to κ-1 and κ̄-1, the respective Debye screening lengths for the exterior and interior of the drop. Using δ = (aκ̄)-1 as a perturbation parameter, we obtain a matched-asymptotic solution that adds corrections through O(δ3) to the flat-plate and Debye-Huckel solutions of the Poisson-Boltzmann equation. In the process, we recover expressions for the drop exterior that constitute an O(δ) improvement over the previously published results. Through a nonlinear transformation of the independent variable, we also derive a uniformly valid approximation that iteratively adds a correction to the flat-plate problem. Each technique yields accurate solutions. For example, the maximum relative error over the drop interior is on the order of 1% for aκ as low as 5 with surface potentials as high as 250 mV. Accuracy improves for larger values of aκ̄, with a maximum relative error below 0.1% for aκ̄ > 15. The asymptotic techniques are also used to obtain expressions for the surface charge density, with equally satisfactory results.
• Rivette, N. J., & Baygents, J. C. (1996). A note on the electrostatic force and torque acting on an isolated body in an electric field. Chemical Engineering Science, 51(23), 5205-5211.
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  Abstract: Expression for the electrostatic force and torque on an isolated body immersed in a dielectric medium have been developed for the case where the imposed electric field is either uniform or varies linearly with position. The expression apply to a body of general shape that carries no net native charge; illustrative examples are provided for ellipsoidal and spheroidal bodies. The force on a body in a uniform field is shown to be zero, which rectifies an incorrect result derived previously by others. The expressions obtained can be adapted to dielectric, leaky dielectric and perfectly conducting bodies subject to either dc or ac forcing fields.
• Rivette, N. J., & Baygents, J. C. (1996). A note on the electrostatic force and torque acting on an isolated body in an electric field. Chemical Engineering Science, 51(Issue 23). doi:10.1016/s0009-2509(96)00337-5
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  Expressions for the electrostatic force and torque on an isolated body immersed in a dielectric medium have been developed for the case where the imposed electric field is either uniform or varies linearly with position. The expressions apply to a body of general shape that carries no net native charge; illustrative examples are provided for ellipsoidal and spheroidal bodies. The force on a body in a uniform field is shown to be zero, which rectifies an incorrect result derived previously by others. The expressions obtained can be adapted to dielectric, leaky dielectric and perfectly conducting bodies subject to either dc or ac forcing fields. Expression for the electrostatic force and torque on an isolated body immersed in a dielectric medium have been developed for the case where the imposed electric field is either uniform or varies linearly with position. The expression apply to a body of general shape that carries no net native charge; illustrative examples are provided for ellipsoidal and spheroidal bodies. The force on a body in a uniform field is shown to be zero, which rectifies an incorrect result derived previously by others. The expressions obtained can be adapted to dielectric, leaky dielectric and perfectly conducting bodies subject to either dc or ac forcing fields.
• Baygents, J. C. (1994). Electrokinetic effects on the dielectric response of colloidal particles: Dielectrophoresis and electrorotation. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 92(1-2), 67-77.
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  Abstract: Electrokinetic effects on a.c. field dielectrophoretic and electrotational phenomena have been examined. Asymptotic methods have been used to carry out computations on the net electric force and torque acting on a spherical colloidal particle and its attending electric double layer. The dielectrophoretic force and the electrorotational torque are shown to depend on the real and imaginary parts of the (complex) particle dipole coefficient respectively. Moreover, it is demonstrated that the dipole coefficient that appears in the force and torque expressions is equivalent to that manifested by the particle in a uniform a.c. field. Thus the force and torque calculations reduce to a problem that has been solved previously in connection with dielectric dispersions in colloidal suspensions. The results for aqueous KCl solutions indicate that at modest ζ potentials (around 25 mV), the dielectrophoretic and electrorotational spectra are influenced strongly by ε{lunate}Pε{lunate}, the ratio of the particle and solution dielectric constants. At higher ζ potentials (100 mV), the spectra of particles with very thin double layers are affected by Stern layer ion transport below forcing frequencies of 1 MHz. © 1994.
• Baygents, J. C. (1994). Electrokinetic effects on the dielectric response of colloidal particles: Dielectrophoresis and electrorotation. Colloids and Surfaces A: Physicochemical and Engineering Aspects, 92(Issue 1-2). doi:10.1016/0927-7757(94)02930-x
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  Electrokinetic effects on a.c. field dielectrophoretic and electrotational phenomena have been examined. Asymptotic methods have been used to carry out computations on the net electric force and torque acting on a spherical colloidal particle and its attending electric double layer. The dielectrophoretic force and the electrorotational torque are shown to depend on the real and imaginary parts of the (complex) particle dipole coefficient respectively. Moreover, it is demonstrated that the dipole coefficient that appears in the force and torque expressions is equivalent to that manifested by the particle in a uniform a.c. field. Thus the force and torque calculations reduce to a problem that has been solved previously in connection with dielectric dispersions in colloidal suspensions. The results for aqueous KCl solutions indicate that at modest ζ potentials (around 25 mV), the dielectrophoretic and electrorotational spectra are influenced strongly by ε{lunate}Pε{lunate}, the ratio of the particle and solution dielectric constants. At higher ζ potentials (100 mV), the spectra of particles with very thin double layers are affected by Stern layer ion transport below forcing frequencies of 1 MHz. © 1994.
• Rosen, L. A., Baygents, J. C., & Saville, D. A. (1993). The interpretation of dielectric response measurements on colloidal dispersions using the dynamic Stern layer model. The Journal of Chemical Physics, 98(5), 4183-4194.
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  Abstract: The standard description of electrokinetic phenomena deals with a particle whose charge is uniformly smeared over its surface and considers ion transport only within a Gouy-Chapman diffuse layer. Experimental studies with colloidal dispersions have shown that this model is not applicable to many systems. To encompass a wider class of behavior, the standard model was extended to include ion migration within the Stern layer, the region between the shear envelope and the rigid particle. Computations show that Stern layer transport increases the conductivity and dielectric response of suspensions as well as the magnitude of the ζ potential inferred from mobility measurements. Model predictions are compared with experimental measurements on two well-defined systems - colloidal silica and a polymer latex. The inclusion of surface transport processes markedly improves agreement between theory and the experimental data. For example, in situations where the standard theory underpredicts the measured dielectric increments by factors of 2 or 3, the dynamic Stern layer model yields results within 5% to 20% of the experimental data at frequencies in the kHz range. © 1993 American Institute of Physics.
• Rosen, L. A., Baygents, J. C., & Saville, D. A. (1993). The interpretation of dielectric response measurements on colloidal dispersions using the dynamic Stern layer model. The Journal of Chemical Physics, 98(Issue 5). doi:10.1063/1.465108
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  The standard description of electrokinetic phenomena deals with a particle whose charge is uniformly smeared over its surface and considers ion transport only within a Gouy-Chapman diffuse layer. Experimental studies with colloidal dispersions have shown that this model is not applicable to many systems. To encompass a wider class of behavior, the standard model was extended to include ion migration within the Stern layer, the region between the shear envelope and the rigid particle. Computations show that Stern layer transport increases the conductivity and dielectric response of suspensions as well as the magnitude of the ζ potential inferred from mobility measurements. Model predictions are compared with experimental measurements on two well-defined systems - colloidal silica and a polymer latex. The inclusion of surface transport processes markedly improves agreement between theory and the experimental data. For example, in situations where the standard theory underpredicts the measured dielectric increments by factors of 2 or 3, the dynamic Stern layer model yields results within 5% to 20% of the experimental data at frequencies in the kHz range. © 1993 American Institute of Physics.
• Baygents, J. C., & Saville, D. A. (1991). Electrophoresis of drops and bubbles. Journal of the Chemical Society, Faraday Transactions, 87(12), 1883-1898.
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  Abstract: We have examined the electrophoresis of drops and bubbles, computing the electrophoretic mobility as a function of the ζ-potential and several other parameters. Our treatment differs from previous work in that we incorporate a more representative picture of the interface. We have found that drops and bubbles are electrophoretically distinct from particles; perhaps the most striking result obtained was that, when the diffuse layers are thin, conducting drops do not always migrate in the direction that would be anticipated from the sign of their surface charge. Thus, the ζ-potential alone is not sufficient to characterize the surface. The analysis shows the sense of the migration is dictated by the net electrochemical stress acting along the interface. For similar reasons, large inviscid spheres tend to remain stationary at modest ζ-potentials and, in contrast to rigid particles, their mobility is actually enhanced by polarization of the double layer. Further, we have uncovered conditions for which the mobility of non-conducting drops is insensitive to the interior viscosity. This 'solidification effect' stems in part from interfacial tension gradients associated with specific adsorption of the ionic solutes, as well as from polarization and, moreover, need not involve the presence of surface-active impurities.
• Baygents, J. C., & Saville, D. A. (1991). Electrophoresis of drops and bubbles. Journal of the Chemical Society, Faraday Transactions, 87(Issue 12). doi:10.1039/ft9918701883
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  We have examined the electrophoresis of drops and bubbles, computing the electrophoretic mobility as a function of the ζ-potential and several other parameters. Our treatment differs from previous work in that we incorporate a more representative picture of the interface. We have found that drops and bubbles are electrophoretically distinct from particles; perhaps the most striking result obtained was that, when the diffuse layers are thin, conducting drops do not always migrate in the direction that would be anticipated from the sign of their surface charge. Thus, the ζ-potential alone is not sufficient to characterize the surface. The analysis shows the sense of the migration is dictated by the net electrochemical stress acting along the interface. For similar reasons, large inviscid spheres tend to remain stationary at modest ζ-potentials and, in contrast to rigid particles, their mobility is actually enhanced by polarization of the double layer. Further, we have uncovered conditions for which the mobility of non-conducting drops is insensitive to the interior viscosity. This 'solidification effect' stems in part from interfacial tension gradients associated with specific adsorption of the ionic solutes, as well as from polarization and, moreover, need not involve the presence of surface-active impurities.
• Baygents, J. C., & Saville, D. A. (1991). Electrophoresis of small particles and fluid globules in weak electrolytes. Journal of Colloid And Interface Science, 146(Issue 1). doi:10.1016/0021-9797(91)90003-q
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  The electrical double layer plays an essential role in the electrokinetic behavior of both rigid and fluid spheres. One of the assumptions woven into the formulation of the classical balance laws of electrokinetics is that the ionogenic solutes are fully ionized. In aqueous media, common inorganic electrolytes such as KCl and NaOH dissociate completely into their constituent ions; the high dielectric constant of water favors dissociation by lowering the energy required to ionize a solute. Not all ionic solutions are aqueous, however, and electrokinetic effects are important in these media, too. Less polar liquids have a much lower dielectric constant, and so they are unable to sustain a high degree of solute ionization; in fact ionogenic solutes may dissociate less than a percent. Here we examine the influence of partial ionization on the electrophoresis of small particles and fluid globules, with a view toward understanding how, and under what conditions, dissociation-association alters the electrokinetics. We find generally that mass-action, consistent with Le Chatelier's principle, works to minimize disturbances to the electrical double layer, resisting polarization of the diffuse ion cloud. Thus, dissociation-association processes are quantitatively important in cases where double layer polarization and relaxation would otherwise prevail. Consequently, the predicted impact on the electrophoretic mobility is greatest for drops and bubbles, since their surfaces are fluid and convection within the interface is a factor. Mass-action can reduce the mobility of a conducting drop by an order of magnitude, and sizeable decreases (50% and more) in drop mobility are even found at ζ-potentials below 50 mV. Rigid particles are affected less dramatically and quantitative effects rarely exceed 10%; particles are markedly insensitive to partial solute ionization unless the ζ-potential is high (above ca. 100 mV) and aκ > 1. The computation scheme employed applies strictly to situations in which the magnitude of the forcing-field is small. Nevertheless, the results imply that for electrokinetic phenomena driven by strong forcing-fields, dissociation-association processes involving ionogenic solutes may be significant in apolar liquids. © 1991.
• Baygents, J., & Saville, D. (1991). Electrophoresis of small particles and fluid globules in weak electrolytes. Journal of Colloid And Interface Science, 146(1), 9-37.
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  Abstract: The electrical double layer plays an essential role in the electrokinetic behavior of both rigid and fluid spheres. One of the assumptions woven into the formulation of the classical balance laws of electrokinetics is that the ionogenic solutes are fully ionized. In aqueous media, common inorganic electrolytes such as KCl and NaOH dissociate completely into their constituent ions; the high dielectric constant of water favors dissociation by lowering the energy required to ionize a solute. Not all ionic solutions are aqueous, however, and electrokinetic effects are important in these media, too. Less polar liquids have a much lower dielectric constant, and so they are unable to sustain a high degree of solute ionization; in fact ionogenic solutes may dissociate less than a percent. Here we examine the influence of partial ionization on the electrophoresis of small particles and fluid globules, with a view toward understanding how, and under what conditions, dissociation-association alters the electrokinetics. We find generally that mass-action, consistent with Le Chatelier's principle, works to minimize disturbances to the electrical double layer, resisting polarization of the diffuse ion cloud. Thus, dissociation-association processes are quantitatively important in cases where double layer polarization and relaxation would otherwise prevail. Consequently, the predicted impact on the electrophoretic mobility is greatest for drops and bubbles, since their surfaces are fluid and convection within the interface is a factor. Mass-action can reduce the mobility of a conducting drop by an order of magnitude, and sizeable decreases (50% and more) in drop mobility are even found at ζ-potentials below 50 mV. Rigid particles are affected less dramatically and quantitative effects rarely exceed 10%; particles are markedly insensitive to partial solute ionization unless the ζ-potential is high (above ca. 100 mV) and aκ > 1. The computation scheme employed applies strictly to situations in which the magnitude of the forcing-field is small. Nevertheless, the results imply that for electrokinetic phenomena driven by strong forcing-fields, dissociation-association processes involving ionogenic solutes may be significant in apolar liquids. © 1991.
• Rhodes, P. H., Snyder, R. S., Roberts, G. O., & Baygents, J. C. (1991). Electrohydrodynamic effects in continuous flow electrophoresis.. Applied and theoretical electrophoresis : the official journal of the International Electrophoresis Society, 2(2-3), 87-91.
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  PMID: 1756188;Abstract: We demonstrate experimentally and theoretically the importance of electrohydrodynamic (EHD) flows in continuous-flow electrophoresis (CFE) separations. These flows are associated with variations in the conductivity or dielectric constant, and are quadratic in the field strength. They appear to be the main cause of extraneous and undesired flows in CFE which have degraded separation performance and have until now not been explained. We discuss the importance of EHD flows relative to other effects. We also describe possible techniques for reducing the associated degradation of CFE separations.
• Rhodes, P. H., Snyder, R. S., Roberts, G. O., & Baygents, J. C. (1991). Electrohydrodynamic effects in continuous flow electrophoresis.. Applied and theoretical electrophoresis : the official journal of the International Electrophoresis Society, 2(Issue 2-3).
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  We demonstrate experimentally and theoretically the importance of electrohydrodynamic (EHD) flows in continuous-flow electrophoresis (CFE) separations. These flows are associated with variations in the conductivity or dielectric constant, and are quadratic in the field strength. They appear to be the main cause of extraneous and undesired flows in CFE which have degraded separation performance and have until now not been explained. We discuss the importance of EHD flows relative to other effects. We also describe possible techniques for reducing the associated degradation of CFE separations.
• Baygents, J. C., & Saville, D. A. (1988). The migration of charged drops and bubbles in electrolyte gradients: diffusiophoresis. PCH PhysicoChemical Hydrodynamics, 10(5/6), 543-560.

Proceedings Publications

• Baygents, J., Rogers, J. J., & Rogers, A. (2020). Effects of High School Dual-Credit Introduction to Engineering Course on First-year Engineering Student Self-efficacy and the Freshman Experience. In 2020 ASEE Virtual Annual Conference, ASEE 2020, 2020-.
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  High school engineering programs and curricula are becoming more widespread partly due to the acceptance of engineering as part of the national PreK-12 science curriculum. Career and Technical Education (CTE) programs often collaborate with community colleges to offer dual credit engineering courses. Additionally, some universities offer for-credit, engineering summer school courses to high school students. Two Advanced Placement (AP) computer science courses are currently taught in high schools and plans are underway for an AP engineering course. As these dual credit programs develop, it is important to understand how they prepare the pathway to an undergraduate engineering major, particularly if they are designed to replace the on campus introduction to engineering course. University engineering first-year programs are critical to the retention and success of engineering students in their freshman year and the wisdom of replacing this first-year experience with a high school course is under debate. Data was collected from 28 first year engineering students at a Hispanic-Serving Institution (HSI) in the American Southwest. All participants took a dual credit introduction to engineering course in high school. Participants were asked about their decision to take the course in high school as well as self-efficacy questions about fitting in, being prepared and about their decision to major in engineering. Sixty-four percent of respondents reported that their high school course made them more prepared than their peers who did not take the high school course. More than 43% reported that their high school engineering course helped them fit in and 53% reported that it made them feel more confident in their decision to major in engineering. Importantly, almost all respondents who did not report a positive effect from their dual credit introduction to engineering course felt neutral about the experience.
• Baygents, J., Rogers, J. J., & Rogers, A. (2019). A Longitudinal Evaluation of an AP Type, Dual-Enrollment Introduction to Engineering Course: Examining Teacher Effect on Student Self-Efficacy and Interest in Engineering (Evaluation). In 126th ASEE Annual Conference and Exposition: Charged Up for the Next 125 Years, ASEE 2019.
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  ENGR 102 HS is an introduction to engineering course taught by 37 high school teachers in both public and private high school classrooms. This university level, dual enrollment course offers high school students three units of credit towards an engineering degree. Unlike an Advanced Placement (AP) class, students who successfully complete the course receive a university transcript. In the ten years since the initial pilot, more than four thousand high school students have taken the course and of those, 2704 students have enrolled and received college credit. With a nearly identical core curriculum as the semester long, ENGR 102 on campus course, the high school program runs for a full school year and thus provides students with increased contact time. Extra classroom time in the high school program allows students to participate in service learning projects, online modules and multiple teacher-designed hands-on projects. Each spring students in the program are asked questions about multiple topics as part of a course evaluation survey. In this longitudinal evaluation, we examine seven years of survey data and report on changes over time in teacher (n=66) effectiveness and explore how teachers influence student self-efficacy and interest in pursuing a career in engineering. The effects of teacher/student gender match was also explored. Teachers with engineering degrees were compared to teachers without and no significant differences were found in effectiveness, course quality or student interest in engineering. However, when students were divided by gender, results showed that female students preferred teachers without the master's in engineering whereas teachers with the master's in engineering were preferred by male students.
• Rogers, J. J., Rogers, A. A., & Baygents, J. C. (2018). Impact of an engineering service learning program on dual credit high school student interests in engineering (evaluation). In 125th ASEE Annual Conference and Exposition, 2018-.
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  Service Learning is a form of experiential education that allows students to apply knowledge learned in the classroom to solve a real community problem. This paper will examine the impact of an EPICS High service learning unit on the interests of high school students. The EPICS High unit is taught as part of a dual credit, introduction to engineering course offered by the University of Arizona. EPICS is a program that was developed at Purdue University to engage undergraduate students in real world engineering problems and to connect engineering with people and the local community needs. Today the EPICS program has been adapted for use in high school classrooms. Data presented in this work were collected over three academic years. Participants were 406 high school juniors and seniors, 325 male and 81 female, who engaged in engineering service projects in their community as part of their ENGR 102 HS course. Data from all ENGR 102 HS students (n=1363) were also examined. Large numbers of participants came from groups typically underrepresented in engineering, including Hispanic students who make up forty percent of the sample. Results showed that EPICS High students who identified as Hispanic/Latino were more likely to express an interest in studying engineering than EPICS High students not identifying as such. Students who identified as Hispanic/Latino who participated in an EPICS high service learning project also showed a stronger interest in studying engineering in college than students of Hispanic/Latino ethnicity in an ENGR 102HS course without the service learning portion. Eighty percent of all the participants reported that participation in the EPICS High unit increased their interest in engineering and no significant gender differences were found. Participants also reported improved capabilities in the areas of teamwork, leadership and communication.
• Rogers, J. J., Rogers, A. A., & Baygents, J. C. (2017). Impact of dual credit introduction to engineering course on female high school students' self-efficacy and decisions to follow a career in engineering (evaluation). In 124th ASEE Annual Conference and Exposition, 2017-.
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  ENGR 102 HS is a dual credit, introduction to engineering course offered in 38 high schools across Arizona and Southern California. ENGR 102 HS is taught by high school teachers in public, charter and private high schools. Since its pilot effort in academic year 2008-09, the ENGR 102 HS program has provided 2,131 high school juniors and seniors with three units of college credit while they explore the field of engineering as a possible career choice. Many young people do not understand what engineering is and the creative work that engineers do. This is why a dual credit introduction to engineering course offered to high school students is so important. ENGR 102 HS curriculum focuses on presenting engineering as a helping profession that improves the human condition. Engineering service learning and biomedical projects are presented to pique the interest of a broad population of students. ENGR 102 HS allows students to try hands-on, design and build projects while still in high school where the risk is low and teacher scaffolding and contact time is high. This broad approach to an introduction to engineering course at the high school level is important to attracting the most diverse, brightest, and creative problem-solvers into the profession. This paper will briefly describe the ENGR 102 HS course curriculum. Five years of student course evaluation survey data (2011-2012 to 2015-2016) for 1469 students both female (N= 289) and male (N=1180) were explored. Statistically significant differences were found in the overall engineering self-efficacy of male and female students using independent sample t-tests. Univariate Analysis of Variance also revealed gender differences in the importance of various elements of self-efficacy to a student's interest in becoming an engineer. Specifically, self-efficacy in traditional STEM coursework predicted interest in becoming an engineer for male but not female students. For female students, experience in the ENGR 102 HS course was found to predict interest in becoming an engineer. This finding demonstrates the positive impact the ENGR 102 HS course has on female students.
• Baygents, J., Hennessey, N., Primeau, R., & Rogers, J. J. (2016). Gender and Self-Efficacy in Engineering: Embracing Failure and a Growth Mindset for Female High School Students (Fundamental). In 123rd ASEE Annual Conference and Exposition, 2016-.
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  Over the last decade much attention has been drawn to the lack of women in engineering careers and the need to attract and retain them in the field. This paper will discuss prior research focused on female student self-efficacy in engineering and the subsequent treatments that have been applied at various stages in the STEM pipeline. Then we will examine the ENGR 102 HS program and results from four years of student course evaluation surveys (n=1093). ENGR 102 High School (HS) is an introduction to engineering course offered in 34 high schools in the Southwest. Students who enroll in the University of Arizona course receive three units of credit from the College of Engineering (COE) towards an engineering degree. Now in its eighth year of operation, the ENGR 102 HS program reaches diverse student populations around the state. ENGR 102 HS looks to fill the pipeline to undergraduate engineering degrees with diverse, capable, informed students of both genders. While gender parity is not our primary objective, we strive to create opportunity, diminish barriers and to deliver a curriculum with a broad appeal. Data analysis for this paper concentrates on selected questions from the ENGR 102 HS course evaluations. Our results examine female (n=220) and male (n=873) high school student responses. Specifically, we explored the landscape of female ENGR 102 HS high school student self-efficacy in engineering to include attitudes towards failure, and mindset. Results demonstrated that female ENGR 102 HS students possessed a significantly lower engineering self-efficacy than male students. With respect to mindset and fear of failure, male and female students showed no statically significant difference.
• Primeau, R., Baygents, J. C., Hennessey, N. K., & Rogers, J. J. (2016, 26-29 June 2016). Gender and self-efficacy in engineering: Embracing failure and a growth mindset for female high school students (Fundamental). In 123rd Annual Conference & Exposition of the American Society of Engineering Education, ISBN 978-0-692-68565-5 ISSN 2153-5965, 19.
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  ENGR 102 High School (HS) is an introduction to engineering course offered in 34 high schools. Students who enroll in the University of Arizona course receive three units of credit from the College of Engineering (COE) towards an engineering degree. Now in its eighth year of operation, the ENGR 102 HS program reaches diverse student populations around the state. ENGR 102 HS looks to fill the pipeline to undergraduate engineering degrees with diverse, capable, informed students of both genders. While gender parity is not necessarily our goal, we strive to create opportunity, diminish barriers and to deliver a curriculum with a broad appeal. Data analysis for this paper concentrates on selected questions from the ENGR 102 HS course evaluations. Our results examine female (n=220) and male (n=873) high school student responses. Specifically, we explored the landscape of female ENGR 102 HS high school student self-efficacy in engineering to include attitudes towards failure, and mindset. Results demonstrated that female ENGR 102 HS students possessed a significantly lower engineering self-efficacy than male students. With respect to mindset and fear of failure, male and female ENGR 102 HS students displayed no statically significant difference.
• Baygents, J., Buxner, S., Hennessey, N., & Rogers, J. J. (2015). GC DELI: A Collection of Online/Hybrid Modules for an Introduction to Engineering Course, Developed for High School and University-level Students (Evaluation). In 2015 122nd ASEE Annual Conference and Exposition, 122.
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  The Grand Challenges: Discover, Explore, Learn and Imagine (GC DELI) online curriculum project at the University of Arizona was developed with a National Science Foundation (NSF), Transforming Undergraduate Education in STEM (TUES) grant. Inspired by the 14 Grand Challenges for Engineering, as defined by the National Academy of Engineering, the goal of the online units is to give freshmen engineering and prospective engineering students an opportunity to explore the broad and socially relevant topics a career in engineering offers. GC DELI unit topics include: Engineering Better Human Health and Providing Access to Clean Water. Students enrolled in the College of Engineering course, Introduction to Engineering (ENGR 102) choose from five online units and study at a self-guided pace. GC DELI units provide students with information about engineering topics that interest them at this critical time in their academic career. The GC DELI project, now in its third year, has recently been adapted for ENGR 102 High School (HS) students. ENGR 102 HS is a three credit, college course taught by high school teachers, to high school students. ENGR 102 HS classrooms have piloted GC DELI units over the past two years. A hybrid version for four of the GC DELI units was developed, providing high school students and their teachers with supplemental hands on projects and other scaffolding. In academic year 2014-15, four hybrid GC DELI units were rolled out to 21 ENGR 102 HS classrooms. This paper contains detailed information about the progress of the GC DELI hybrid units in high schools, responses to forced-choice questions and qualitative data from teachers who have worked with the units. Additionally, we include responses to forced-choice questions from the 31 student evaluations collected after delivery of one hybrid GC DELI unit.
• Rogers, J. J., Hennessey, N. K., Buxner, S., Baygents, J. C., Buxner, S. R., Hennessey, N. K., & Rogers, J. J. (2015, 14-17 June 2015). GC DELI: A Collection of Online/Hybrid Modules for an Introduction to Engineering Course, Developed for High School and University-level Students (Evaluation). In Proceedings of the 122nd Annual Conference & Exposition of the American Society of Engineering Education, ISBN 978-0-692-50180-1 ISSN 2153-5965, 26.811.1 - 26.811.27.
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  Description and characterization of online curriculum modules inspired by the 14 Grand Challenges for Engineering (as defined by the National Academy of Engineering), referred to locally as the GC DELI--Grand Challenges: Discover, Explore, Learn, Imagine. The goal of the initiative is to give first-year and prospective engineering students an opportunity to explore the broad and socially relevant topics a career in engineering might offer. 
• Baygents, J., Goldberg, J., Rogers, J. J., & Vezino, B. (2014). ENGR 102 for High School: An Introduction to Engineering, AP type course taught in high schools by high school teachers. In 121st ASEE Annual Conference and Exposition: 360 Degrees of Engineering Education.
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  In fall 2008, twenty-one students from Hamilton High School in Chandler, Arizona participated in a University of Arizona pilot program and were enrolled in a course called ENGR 102 HS. This introductory engineering course offers students three units of credit towards an engineering degree. Since the initial pilot, 1218 high school students have enrolled and received college credit for the course. With a nearly identical core curriculum as the semester long, on campus version of ENGR 102, the high school program runs for a full school year and thus provides the increased contact time and teacher assistance many high school students require. Extra classroom time in the high school program allows students to participate in service learning projects, online modules and teacher designed, hands-on projects. High school teachers that are selected to teach ENGR 102 HS tend to have engineering backgrounds; however, many of the most successful teachers in the program teach math or science at their high school and succeed due to a personal enthusiasm for the topic. A week long teacher training workshop is held each summer to prepare new teachers to deliver the core curriculum. Returning teachers attend an annual three day training to share ideas, mentor new teachers, receive new classroom content and to strengthen the dynamic ENGR 102 HS community of engineering educators. Seed funding for ENGR 102 HS program development and logistical sustainability was provided during the first four years of the program. Now in its sixth year, ENGR 102 HS operates primarily on tuition dollars and has programs operating in two states, 29 diverse high schools, within 15 different school districts and 30 teachers deliver the course to over 450 students. 301 of the 450 students in the 2013-14 cohort took ENGR 102 HS for University of Arizona credit. This paper will discuss ENGR 102 HS program history, core curriculum, spin-off research and development, keys to success, teacher training and program logistics. © American Society for Engineering Education, 2014.
• Vezino, B. R., Baygents, J. C., Goldberg, J. B., & Rogers, J. J. (2014, 15-18 June 2014). ENGR 102 for high school: An Introduction to Engineering, AP type course taught in high schools by high school teachers. In Proceedings of the 121th Annual Conference & Exposition of the American Society of Engineering Education, ISSN 2153-5965, 24.518.1 - 24.518.19.
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  Description and charcterization of University of Arizona's ENGR102 HS course, six years into the program. Included are: program mission and history; spin off research and development; teacher training program logistics; keys to success and program outcomes.
• Baygents, J., & Hunter, J. (2013). Grand Challenges DELI (Discover, Explore, Learn, Imagine) Project. In 120th ASEE Annual Conference and Exposition.
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  Here we report on data collected for a project in which five new web-based lines of study, referred to as Elective Units, were developed by engineering faculty members with expertise in topics related to the NAE Grand Challenges.1 In a previous communication,2 we described the rationale, development scheme and topical content of the Elective Units. In this work we summarize selected results for the first full-scale offering of the Elective Units to a large cohort of students (400+) enrolled in an undergraduate engineering program. The Units were designed to give freshmen and prospective engineering students, many of whom are still in high school, an opportunity to explore topics of their choice in the engineering foundation course, Introduction to Engineering, offered by the University of Arizona (UA). The selection of topics was based on a Grand Challenges Interest Survey administered to 100+ freshmen engineering students, as part of the groundwork for the project. Students participating in the Interest Survey were asked to investigate the fourteen Grand Challenges for Engineering established by the National Academy of Engineering and indicate which challenges captured their interests. The five new Elective Units were modeled after a pilot Unit that was developed and successfully delivered in Spring 2010 as a result of a Learner-Centered Course Redesign Innovation Grant, funded by the Arizona Board of Regents. The learning in the Units is experiential in that each Unit allows students to address, first-hand, various types of problems that engineers attempt to solve. The activities require students to use a variety of tools to investigate the topics in order to establish a foundation of knowledge. Students are encouraged to further investigate topics and make connections to the societal, global, environmental and economic context that frame the Grand Challenge. The assignments are designed to motivate students to engage in higher-level thinking. Vignettes, i.e. short videos, describing each challenge and emphasizing the important role that engineers play in solving these challenges, were recorded. In addition, detailed written descriptions of the Units were developed. Students use the vignettes and reference materials to decide which Elective Unit(s) they wish to study. They then have the opportunity to devote four weeks of the semester, roughly one Carnegie unit of effort, to the exploration of the topic by making use of the cyberinfrastructure. © American Society for Engineering Education, 2013.
• Baygents, J., Dexter, P., Hunter, J., Oakes, W., & Thompson, M. (2012). Early Engineering through Service-learning: Adapting a University Model to High School. In 119th ASEE Annual Conference and Exposition.
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  The challenges of this next century require a new generation of engineering talent. In the United States, interest in engineering has remained flat and many groups within remain underrepresented relative to the overall population, specifically women and ethnic minorities. Attracting the next generation of diverse engineers requires a diverse set of pre-college experiences to connect diverse pathways leading to an engineering degree. One exciting approach is the use of service-learning to expose students to design and engineering. Servicelearning has been well established in many disciplines with positive impacts on interest, motivation, student satisfaction, personal success, desire, and retention of students who participated in service-learning projects. Service-learning is pedagogically consistent with literature on the recruitment and retention of women and other underrepresented groups in science and engineering. These benefits have been studied at the higher education level and show promise for pre-college as well. Service-learning connected to engineering also has an enormous potential for capitalizing on the wave of interest in community engagement among teenagers nationally. Connecting service to our community with engineering aligns perfectly with the National Academy's Changing the Conversation. This paper describes the adaptation of a successful university model to high school having been disseminated to more than 50 schools in 10 states. This paper highlights high school programs that have been integrated into the school day and are supported by a large Midwestern university and two large Southwestern universities. Example projects are described as well as the academic structure and teacher training processes. Demographic data shows that the model is attracting more female students and students from groups traditionally underrepresented in engineering. Data also shows that students are becoming more interested in engineering as a result of their experience in the service-learning programs. © 2012 American Society for Engineering Education.
• Baygents, J., Goldberg, J., & Hunter, J. (2011, 26-29 June 2011). Development of the Supply Chain: An AP Engineering Experience for High School Students at the State Level. In 118th Annual Conference & Exposition of the American Society of Engineering Education, ISSN: 2153-5965, 22.498.1 - 22.498.15.
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  We describe and characterize a pilot project in which a college of engineering at a major public research university offers their Introduction to Engineering course at high schools throughout the State. At the high school (HS), the course is taught by HS teachers who are appointed adjunct instructors by the college. The participating instructors typically have experience teaching AP calculus or science or, alternatively, CTE engineering courses. The adjuncts receive two-weeks training from university faculty members who have offered the on-campus version of the class, hereafter referred to as ENGR 102. Curriculum is supplied by the college and the HS instructors are given the freedom to supplement the curriculum with their own materials (most do). The HS students are admitted to the university as non-degree-seeking students and register for three units of university credit. Students are recruited into the course by the HS instructor acting locally. The course is targeted toward HS seniors who have previously exhibited an interest and proficiency in math and science.
• Jiang, L., Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Zheng, X. J., & Zohar, Y. (2011). Dynamic states of adhering cancer cells under shear flow in an antibody-functionalized microchannel. In 2011 IEEE 24th International Conference on Micro Electro Mechanical Systems, 849-852.
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  Dynamic states of cancer cells moving under shear flow in an antibody-functionalized microchannel are investigated experimentally and theoretically. A simplified physical model was adopted to analyze the cell motion; it features a rigid sphere, with receptors on its surface, moving above a solid surface with distributed ligands. The cell motion is described by the Langevin equation where the hydrodynamic interactions, gravitational drift force, receptor-ligand binding force, and thermal fluctuations are all taken into account. The receptor-ligand bonds are modeled as Hookean springs. In this study, three dynamic states of cell motion have been identified: (i) free motion, (ii) rolling adhesion, and (iii) firm adhesion depending on the flow shear rate. The numerical simulations allow exploring effects of numerous parameters such as cell-receptor and surface-ligand density.
• Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Wang, L., Zheng, X. J., & Zohar, Y. (2010). Quantitative specific binding of breast cancer cells in an antibody-functionalized microchamber array. In 2010 IEEE 23rd International Conference on Micro Electro Mechanical Systems (MEMS), 939-942.
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  The system performance of an antibody-functionalized microchamber array, developed for selectively binding target cancer cells, is quantitatively characterized. The devices are designed to allow accurate counting of loaded and captured cells from heterogeneous suspensions. Specific interaction between cancer cell receptors and immobilized surface ligands has been demonstrated under static conditions. Performance measures such as specificity, sensitivity and accuracy are uniquely defined and experimentally evaluated. Several cell mixtures have been tested, and the quantitative system performance criteria are reported as a function of cell concentrations in the tested suspensions. These criteria provide a critical quantitative basis for a comparison among different systems aimed at selectively isolating target bio-species from complex mixtures.
• Baygents, J. C., Cheung, L. S., Guzman, R., Heimark, R. L., Schroeder, J. A., Stopa, A., Zheng, X. J., & Zohar, Y. (2009). Flow Acceleration Effect on Cancer Cell Deformation and Detachment. In 2009 IEEE 22nd International Conference on Micro Electro Mechanical Systems, 431-434.
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  The effect of flow acceleration, rather than just the flow rate, on the response of an attached cancer cell is for the first time reported. Selective binding of prostate cancer cells to a surface functionalized with anti-N-cadherin antibodies utilizing a microfluidic system under flow conditions has been studied [1]. Here, the behavior of a captured cell under a time-dependent flow field is investigated experimentally and numerically. Under slowly increasing flow rate, the cell deformation is more pronounced resulting in lower drag force on attached cells. Furthermore, the contact area between the cell and the functionalized surface is larger, potentially enhancing the cell adhesion force. Consequently, a higher flow rate is required to detach cells exposed to such a flow field. Numerical simulations have been utilized in effort to quantify the required detachment force. The results confirm that to obtain a similar shear stress, a higher flow rate is needed for attached cells under lower flow acceleration.
• Baygents, J. C., Cheung, S. L., Guzman, R., Heimark, R. L., Schroeder, J. A., Wang, L., Zheng, X., & Zohar, Y. (2009). Specific Binding of Cancer Cells Using a Microchamber Array Functionalized With Antibodies. In Volume 12: Micro and Nano Systems, Parts A and B, 12, 821-827.
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  Specific binding of target suspended metastatic cancer cells to an antibody-functionalized surface utilizing a microfluidic device has experimentally been investigated under various conditions. The microfluidic devices, fabricated in silicon using DRIE process, consisted of a 5×5 micochamber array; each 1mm×1mm in area, and 50μm in depth. The oxide surface of the microchammber array was functionalized with various antibodies immobilized on a protein G layer. The microfluidic device design allows accurate counting of cells loaded into each microchamber and, thus, enabling a reliable counting of cells captured from homogeneous suspensions. The effects of cell suspension concentration, incubation times and ambient temperature on cell capture efficiency have been examined. Furthermore, to evaluate the specificity of the cell-surface interaction, several cell cancer types expressing different membrane receptors have been incubated on surfaces functionalized with various counter receptors. Specific binding of up to 100% of the suspended cells is observed when using surfaces functionalized with counter receptors matching the cell receptors; otherwise, non-specific binding of less than 15% of suspended cells is obtained if the functionalized counter receptors do not match the cell receptors.Copyright © 2009 by ASME
• Chaplin, B. P., Gu, Z., Baygents, J. C., & Farrell, J. (2008). Electrochemical regeneration of ion exchange (ERIX). In American Chemical Society Division of Environmental Chemistry Preprints of Extended Abstracts 2008, 48.
• Cheung, L. S., Zheng, X. J., Stopa, A., Schroeder, J., Hemark, R. L., Baygents, J. C., Guzman, R., & Zohar, Y. (2008). Attachment & detachment of prostate cancer cells in a microfluidic system. In 12th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2008.
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  Cadherins make up a family of cell adhesion molecules, and one cadherin subtype only interacts with its counter receptor. Cancer cells typically down-regulate Ecadherin and up-regulate N-cadherin. Hence, a microchannel-based system is developed, with immobilized anti-N-cadherin antibodies, for highly specific capture of prostate cancer cells under both static (no-flow) and dynamic (flow) conditions. The maximum number of detached cells, after capture, is found to depend not only on the flow-induced shear stress but also on the rate of change of the applied shear stress. © 2008 CBMS.
• Cheung, L. S., Zheng, X., Stopa, A., Schroeder, J. A., Heimark, R. L., Baygents, J. C., Guzman, R. Z., & Zohar, Y. (2008, 12-18 October 2008). ATTACHMENT & DETACHMENT OF PROSTATE CANCER CELLS IN A MICROFLUIDIC SYSTEM. In 12th International Conference of Minaturized Systems for Chemistry and Life Sciences (μTAS 2008), Paper No. T33F.
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  Cadherins make up a family of cell adhesion molecules, and one cadherin subtype only interacts with its counter receptor. Cancer cells typically down-regulate Ecadherin and up-regulate N-cadherin. Hence, a microchannel-based system is developed, with immobilized anti-N-cadherin antibodies, for highly specific capture of prostate cancer cells under both static (no-flow) and dynamic (flow) conditions. The maximum number of detached cells, after capture, is found to depend not only on the flow-induced shear stress but also on the rate of change of the applied shear stress.
• Lee, L. M., Heimark, R. L., Baygents, J. C., & Zohar, Y. (2005). Photolithographic patterning of multiproteins on a single chip using low-meltingpoint agarose as a protection layer. In 9th International Conference on Miniaturized Systems for Chemistry and Life Sciences, MicroTAS 2005, 1.
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  This paper presents a novel technology, based on low-melting-point (L.M.P.) agarose as a protection layer and oxygen plasma etching, for photolithographic patterning of two different proteins on a single chip. Following the patterning of the first protein layer, the second protein layer is immobilized on the un-protected regions. Both protein layers are shown to be active at the end of the fabrication process. Copyright © 2005 by the Transducer Research Foundation, Inc.
• Lee, L. M., Heimark, R. L., Baygents, J. C., & Zohar, Y. (2005). Self-aligned immobilization of proteins on silicon dioxide surfaces. In 05AIChE: 2005 AIChE Annual Meeting and Fall Showcase.
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  In the last decade, the field of Bio-MEMS has emerged as an application using both microsystem technology and biotechnology. Novel surface nanotechnologies have been developed to selectively modify artificial surfaces with active bio-layers to be used for biosensors, cell studies and tissue engineering. These methods include local deposition of bio-molecules using ink-jet, laser ablation, vapor deposition, photochemical structuring and photolithography techniques. Currently, the most popular technique is contact printing, where the printing process allows the transfer of molecules to various surfaces in a wide concentration range with high efficiency. However, this may not be an attractive method if a precise alignment to prefabricated fine features is required or if precise immobilization of different proteins on the same chip is needed. Photolithography is a well-established technique in batch fabrication of ICs with high resolution and precise alignment. Patterns are transferred from a mask to a photoresist layer-and from the photoresist to a thin film of bio-molecules immobilized on a surface. However, the solutions used to develop and strip the photoresist layer lead to stability problems for functional proteins. In this work, we utilized standard photolithographic procedures to generate stable patterns consisting of a functional protein (protein A + IgG antibody) next to end-grafted PEG self-assembled monolayers on silicon dioxide surfaces. The PEG patterns were generated using the lift-off method, while the immobilized proteins were self-aligned on the surface not protected by the PEG layer. Both the PEG and the protein layers have been characterized by demonstrating their proper functionality at the end of the fabrication process. Physical characterization of the surface modifications included optical microscopy, contact angle measurements, and AFM profiling. Protein patterns were shown to be biologically active by the selective (antibody-antigen) binding of microparticles covered with IgG antigen; typically, selectivities on the order of 0.96 were obtained.
• Lee, L. M., Heimark, R. L., Baygents, J. C., Zohar, Y., & Lee, L. M. (2005, 9-13 October 2005). Photolithographic patterning of multiproteins on a single chip using low-meltingpoint agarose as a protection layer. In 9th International Conference on Miniaturized Sytems for Chemistry and Life Sciences (μTAS 2005), Paper No. 0379.
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  Photolithographic patterning of proteins (from aqueous solutions) onto a single chip (glass substrate) using low-melting-point agarose as a protective mask/shield to preserve protein functionality that would otherwise be compromised by lithographic processes.
• Sounart, T. L., & Baygents, J. C. (2001, 3-6 October 2000). Electrically-driven fluid motion in channels with streamwise gradients of the electrical conductivity. In Electrokinetic Phenomena 2000, 195, 59–75.
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  Electroosmotic motion through charged, narrow-bore channels and capillaries is analyzed for the case where there are dominantly-axial gradients in the composition of the flowing electrolyte. The channel width is assumed to be large compared with the Debye screening length, and the electroosmotic slip velocity along the channel wall is taken to vary locally with the ionic strength, pH and electric field. Owing to the wall slip condition, the velocity distribution is nonlinearly coupled to the composition variations within the fluid. The prototype problem studied is one in which buffer ions and other solutes (e.g. analytes) are initially distributed in a sample zone that is sandwiched between uniform running buffer. For the situations considered, the conductivity of the sample zone differs significantly from that of the running buffer; such configurations are common to stacking and electroosmotic pumping protocols. In a frame of reference that moves with the mean velocity of the flow, the velocity field exhibits flow separation in the neighborhood of the conductivity variations and this gives rise to solutal mixing and dispersion in and about the sample zone. Copyright © 2001 Elsevier Science B.V.
• Erker, J. A., & Baygents, J. C. (1996, July). Electrohydrodynamic Interaction of a Pair of Spherical Drops. In Proceedings of the 3rd Microgravity Fluid Physics Conference, NASA Conference Publication 3338, pp. 731–736.
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  The axisymmetric electrohydrodynamic interaction between two spherical emulsion drops has been examined, using the leaky dielectric model to represent the constitutive behavior of the liquid phases. The results follow from the general solutions in bispherical coordinates to the Laplace equation for the electric potential and the Stokes equations for the velocity field. For drops of similar composition, the electrical interactions induced between the drops by the imposition of the electric field are always attractive, meaning they favor coalescence of the drop pair. The hydrodynamic interactions, however, are not always favorable and, indeed, are shown in certain circumstances to drive the drops apart.
• Glynn, J. R., Arnold, R. G., Ogden, K. L., & Baygents, J. C. (1996, July). Electrokinetic characterization of the transport behavior of monoclonal bacterial populations in porous media. In Proceedings of the 5th World Congress of Chemical Engineering, III, pp. 689–693.
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  Bacterial transport in porous media is central to a variety of contemporary environmental issues. For example, plumes of pathogenic microorganisms may threaten drinking water supplies after an unintentional injection of reclaimed wastewater to aquifers. Conversely, microorganisms with unusual metabolic capabilities can be introduced into the subsurface to remediate hazardous contaminants. In this paper, we discuss the use of capillary electrophoresis measurements to help characterize bacterial adsorption, a key factor in bacterial transport. 14 refs., 3 figs.