Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session ZC24: Electrokinetic Transport III |
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Chair: Ankur Gupta, University of Colorado, Boulder Room: 150A |
Tuesday, November 21, 2023 12:50PM - 1:03PM |
ZC24.00001: Abstract Withdrawn
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Tuesday, November 21, 2023 1:03PM - 1:16PM |
ZC24.00002: Diffusiophoretic Behavior of Polyelectrolyte Coated Particles Burak Akdeniz, Jeffery A Wood, Rob Lammertink Diffusiophoresis is the movement of particles under a solute concentration gradient. This occurs due to the generation of fluid flow at the solid-liquid interface: diffusio-osmosis (counter diffusiophoresis). In electrolyte diffusiophoresis, the particle velocity is described by the relative electrolyte gradient and the diffusiophoretic mobility, which depends on both the zeta potential of the particle and the diffusivity contrast between electrolyte cations and anions. Spatial and temporal variations in electrolyte concentration in experimental systems can lead to variations in the zeta potential of particles, which can have a large influence on diffusiophoretic behavior. Here, we show that adsorption of a single bilayer of the polyelectrolyte pair (PDADMAC/PSS) on the particle surface results in effectively constant zeta potential values with respect to electrolyte concentration, allowing a constant potential assumption to describe the experimental observations. Moreover, we show that the concentration of background salt during the coating process of the polyelectrolyte pairs plays a critical role in the final near-constant value of particle zeta potential obtained. This work highlights the utility of using simple polyelectrolyte pairs to tune the zeta potential and maintain constant values for precise control of diffusiophoretic transport during experimental observations. |
Tuesday, November 21, 2023 1:16PM - 1:29PM |
ZC24.00003: Non-equilibrium gel formation in suspensions of conductive particles in electric field Seyed Mohammad Hosseini, Siamak Mirfendereski, Jae Sung Park In flow batteries, incorporating very small (~20 nm) conductive particles, such as carbon black, into a battery slurry can enhance the charge transport while triggering a depletion-attraction interaction among larger (~1 micron) active particles inside a slurry solution. To investigate this effect, we utilize large-scale numerical simulations to study the behavior of suspensions of ideally conductive particles in an electric field with an attractive potential energy. These suspensions are known to undergo two nonlinear electrokinetics, namely induced-charge electrophoresis (ICEP) and dielectrophoresis (DEP), where ICEP is predominant over DEP for ideally conductive particles. A gel state is determined based on the average number of interparticle bonds. At low field strengths, a non-equilibrium gel is formed due to strong attractive interactions. As the field strength increases, the gel begins to break and reform while maintaining gel states as its average bond number remains almost the same. At sufficiently high field strengths, the electrokinetic effects become dominant to disrupt the bond formation, which is no longer in a gel state. A phase diagram for a universal gel line in terms of the field strength and volume fraction is drawn and compared to colloidal gels. |
Tuesday, November 21, 2023 1:29PM - 1:42PM |
ZC24.00004: Asymmetric rectified electric and concentration fields in multicomponent electrolytes with surface reactions Nathan Jarvey, Filipe H Henrique, Ankur Gupta
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Tuesday, November 21, 2023 1:42PM - 1:55PM |
ZC24.00005: Ionic wind induced fine particle removing propeller Yeawan Lee, Dae Hoon Park, Gunhee Lee, Inyong Park, Jin-Tae Kim, Kee-Jung Hong, Bangwoo Han, Sang-Bok Kim A novel ionic wind induced rotating propeller to remove fine particulate matter is developed. Ionic wind generated by corona discharge, which is a non-thermal atmospheric plasma phenomenon, has beed studied for at least one century because of its promising applications such as aerial vehicle, electrostatic precipitation, electronics cooling, and electro-spray. Herein we designed a electrohydrodynamic rotating propeller using pin emitter-to-cylindrical collector discharge system. The propeller rotates due to the air ions produced by the pin emitter attached to the propeller. The air ions not only generate thrust but also charge airborne particles. For the parametric study, the rotational motion was analyzed by varing the height and position of the pin emitter, discharge current, and applied votage by experiment. Computational simuation was also provided to analyze electric field. Finally, the particle removing performance and the flow rate of the rotating propeller was evaluated for industrial application. |
Tuesday, November 21, 2023 1:55PM - 2:08PM |
ZC24.00006: Electrohydrodynamic lift-off from the electrode of a colloidal particle suspended in a non-polar fluid Zhanwen Wang, Michael J Miksis, Petia M Vlahovska A charge-neutral colloid is electrostatically attracted by a nearby electrode. However, electrohydrodynamic (EHD) flows can induce lift and particle detachment from the electrode. In aqueous electrolyte solutions, an ICEO-type flow due to action of the electric filed (perturbed by the particle) on the charge in the polarization layer near the electrode can cause the colloid lift-off. In this talk, we show that in a non-polar fluid the Onsager effect (field-dependent rate of ion pair dissociation) can give rise to a non-uniform conductivity and a bulk electric charge. The resulting EHD flow scales with the cube of the magnitude of the applied field. Under the assumption of zero Reynolds number, the lift force on the particle is calculated using the Lorentz reciprocal theorem. The results indicate that the lift decays as the inverse square of the distance between the particle and the electrode, much slower than the EHD lift in aqueous solutions. |
Tuesday, November 21, 2023 2:08PM - 2:21PM |
ZC24.00007: Electrokinetic flows and surface conductivity on plain and nanostructured surfaces Austin Dick, Aktaruzzaman Al Hossain, Carlos E Colosqui At very low ionic strengths below 1 mM, for which the electrical conductivity of the electrolyte solution is extremely small, so-called surface conductivity due to nontrivial interfacial phenomena becomes the dominant contribution to the micro/nanochannel electrical conductance. This effect is detrimental for many important applications of electrokinetic flows using micro/nanofluidic devices that operate with low electrolyte concentrations. This talk will present recent experimental and theoretical results on the effect that the nanoscale surface topography has on the electrical surface conductivity over a wide range of ionic strengths (0.01 to 10 mM) for aqueous solutions of 1:1 electrolytes in slit micro/nanochannels with hydrophilic and hydrophobic surfaces. The presented results provide new insights on the diverse electrokinetic phenomena (e.g., Stern layer and interfacial ion mobility) that controls the surface conductivity observed in slit micro/nanochannels, and propose simple strategies to control it or reduce it when desired. |
Tuesday, November 21, 2023 2:21PM - 2:34PM |
ZC24.00008: Abstract Withdrawn
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Tuesday, November 21, 2023 2:34PM - 2:47PM |
ZC24.00009: Isotachophoresis with oscillating sample zones to control the mixing of co-focused species Florian Gebhard, Henning Bonart, Tamal Roy, Steffen Hardt Microfluidic isotachophoresis (ITP) is a powerful technique that can significantly increase the reaction rate of low-concentration species by co-focusing them in a narrow sample zone. It uses strong gradients in the electric field between two electrolytes to increase the local concentration of the reactants by several orders of magnitude. Therefore, ITP has been utilized to reduce the reaction time in various bioanalytical assays. However, in conventional ITP, it is hardly possible to manipulate the spatial distribution of the reacting species and thus to control the course of a reaction. Here we present experiments that introduce a new approach to compensate this disadvantage. Two samples are initially focused and separated by a spacer in ITP with a DC electric field. By superimposing an oscillating field component with sufficiently high amplitude to the DC field, the spatial overlap of their concentration profiles, i.e. their mixing, is temporarily increased due to electromigration dispersion. The time average of this overlap can be precisely controlled by varying the frequency and amplitude of the oscillation. We suggest that this can be transferred to reactions involving ionic species with sufficiently different electrophoretic mobilities. Tuning the parameters of the oscillatory electric field should allow to directly influence the corresponding reaction rate. |
Tuesday, November 21, 2023 2:47PM - 3:00PM |
ZC24.00010: Diffusiophoresis as a mechanism to study human population migration patterns Benjamin Alessio, Ankur Gupta Drawing inspiration from diffusiophoresis in colloids and chemotaxis in a bacteria, we propose that human populations exhibit a similar migratory behavior, albeit on significantly larger timescales and length-scales, driven by gradients of ”attractants” such as economic opportunities, political viewpoints, and safety, among other factors. To explore this idea, we present a novel reaction-diffusion-migration (RDM) framework, which produces features not achievable through reaction-diffusion alone. We study different attractant landscape scenarios such as externally driven, autocatalytic driven and feedback driven. We observe novel features arising from the RDM framework such as negative diffusion tendencies of populations to cluster around a hotspot, highly segregated population distributions and traveling wave solutions. We discuss the potential of the RDM framework in elucidating broader patterns of population migration and the emergence of hotspots. |
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