Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session A32: Electrokinetic Transport I |
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Chair: Siddhartha Das, University of Maryland Room: 158AB |
Sunday, November 19, 2023 8:00AM - 8:13AM |
A32.00001: Effect of Electric Field Mediated Fluid Thickening on Electrokinetics over Charge - Modulated Interfaces Anindita Bhattacharya, Jyotirmoy Bhattacharya, Suman Chakraborty We develop a model to describe ion transport , in micro- and nanochannels with variable surface charge, taking into account electric- field mediated fluid thickening ( viscoelectric effect). In our cross- sectionally averaged model, the effects of electric double layer on the axial transport are taken into account via modifications in the classical Poisson- Boltzmann theory. The effect of viscoelectricity is taken into account for different characteristic length scales of the EDL resulting in distinctive features for overlapped and non- overlapped EDLs. We also consider the effect of the axial pitch of surface charge modulation on the concentration profiles along the central axis of the channel. We relate our findings on the effect of heterogeneous surface charge on the velocity profile on the fluidic confinement. We also calculate the induced pressure gradient from the force balance considerations. On comparing the induced pressure gradient for flows with and without viscoelectric effect, our results reveal that the induced pressure gradient is more for the former, deciphering- unravelled interplay of electromechanical and hydrodynamics over charge- modulated interfaces. |
Sunday, November 19, 2023 8:13AM - 8:26AM |
A32.00002: Diffusiophoresis of a spherical particle in porous media Henry Chu, Siddharth Sambamoorthy Diffusiophoresis refers to the deterministic motion of particles induced by a surrounding concentration gradient of solutes. Recent experiments demonstrated and measured colloid diffusiophoresis in porous media, but existing theories cannot predict the observed colloid motion. In this work, we develop a mathematical model that can predict the diffusiophoretic mobility of a charged colloidal particle driven by a binary monovalent electrolyte concentration gradient in porous media. The porous medium is modeled as a Brinkman medium with a constant Darcy permeability. The linearized Poisson-Boltzmann equation is invoked to model a weakly or moderately charged particle. We report three new significant findings. First, compared to diffusiophoresis in a free electrolyte solution, we show that the particle mobility could be significantly hampered by a porous medium due to the additional hydrodynamic drag. Second, we demonstrate that particle diffusiophoresis in response to a change in the electrolyte concentration in a porous medium could be qualitatively different from that in a free electrolyte solution. Third, a comparison between our model predictions and experiments demonstrates excellent agreements within the scope of the model, highlighting the predictive power of the model. The mathematical developed here could be employed to design diffusiophoretic colloid transport in porous media, which are central to applications such as nanoparticle drug delivery and enhanced oil recovery. |
Sunday, November 19, 2023 8:26AM - 8:39AM |
A32.00003: Electrokinetic cell powered by osmotic gradients: an analytic survey for asymmetric wall potentials and hydrophobic surfaces Guillermo Sanchez, Federico Mendez, Edgar Ramos Nowadays the fabrication of MEMs (microelectromechanical systems) has given rise to several studies whose main purpose is obtaining the greater benefit of micro-nano scales putting special interest in the improvement of the design of such devices. One of several applications is harvesting energy due to electrokinetic phenomena, more specifically, streaming potential. Nonetheless, there is a lack of theoretical studies encompassing coupled asymmetries in both slip conditions and electric potentials (these being associated with the chemical and physical characteristics of the surfaces). In virtue of the previous explanation, ideal assumptions based on the symmetry of some variables must be reconsidered, especially when manufacturing symmetric flat surfaces on a tiny scale is quite difficult to achieve. |
Sunday, November 19, 2023 8:39AM - 8:52AM |
A32.00004: Simultaneous Desalination and Hydrogen Production by Nanoelectrokinetic Selective Ion Separation Yoon Sehyuk, Sungjae Ha, Jihee Park, Sung Jae Kim To address ‘Water-Energy Nexus’ challenges, we aim to develop a novel system enabling simultaneous desalination and hydrogen production by precisely regulating nanoelectrokinetic ion transport through ion exchange membranes within a micro-nanofluidic platform. Applying voltage to a cation exchange membrane, which permits the passage of only cations, leads to the creation of an ion depletion zone (IDZ) on the anodic side and an ion enrichment zone (IEZ) on the cathodic side of the membrane, known as Ion Concentration Polarization (ICP) phenomenon. Our key strategy is to produce desalted water from the IDZ and simultaneously produce hydrogen at the reduction electrode. Using microfluidic channels connected with a cation exchange membrane and microelectrodes, we visualize the generation of acidic brine suitable for hydrogen production at the IEZ (i.e. gas bubbles at the reduction electrode), during desalination at the IDZ. Furthermore, we analyze and control the transport of Na+ and H+ ions competing through the membrane within highly branched microchannels under various operating conditions. This nanoelectrokinetic study for the ion transport through the ion exchange membrane will play a key role in realizing simultaneous water desalination and electrolytic hydrogen production. |
Sunday, November 19, 2023 8:52AM - 9:05AM |
A32.00005: Effect of polymer-particle interactions on diffusiophoresis of latex particles Viet Sang Doan, Tanja Riess, Sangwoo Shin In this study, we experimentally investigate the impacts of polymer-particle interactions on the diffusiophoresis of polystyrene microspheres. Using a microfluidic setup, we reveal how the background polymers surrounding a charged particle dictate the diffusiophoretic motion of the particle. For non-adsorbing polymers, the depletion of polymer chains near the particle surface via steric exclusion alters the local viscosity of the Debye layer, which is distinct from the bulk, thereby directly affecting the diffusiophoretic flow. On the other hand, adsorbing polymers affect particle diffusiophoresis by reducing the effective thickness of the Debye layer. While the polymer adsorption or depletion leads to a monotonic change in the particle mobility with respect to the varying degree of each effect, we observe non-monotonic mobility when the migrating particles are under the simultaneous influence of both the polymer depletion and adsorption. Our findings reveal significant roles played by the relative difference between the polymer size and the effective Debye screening length in determining the observed particle motion, thus providing valuable insights into particle phoretic transport in complex environments. |
Sunday, November 19, 2023 9:05AM - 9:18AM |
A32.00006: Droplet electromigration beyond the Taylor-Melcher model explained through the strong-electrolyte limit Philipp G Marthaler, Andreas G Class The control of fluid droplets inside a microfluidic system relies heavily on the predictability of their behavior in the presence of electric fields. Traditional models, such as the Taylor-Melcher model, capture electromigration observed in experimental studies only under certain conditions. |
Sunday, November 19, 2023 9:18AM - 9:31AM |
A32.00007: Kirchhoff's Laws Based on Electrochemical Potential of Charge Dictate Double-Layer Charging in Porous Media Filipe H Henrique, Pawel J Zuk, Ankur Gupta 3D-printed electrode structures are a promising avenue for advancing next-generation miniaturized energy storage devices. However, a rational approach to designing such electrodes remains elusive since direct numerical simulations of transport in these complex geometries are prohibitively expensive. We address these limitations by developing a Debye-Hückel model to describe the electric double-layer charging of a binary electrolyte in an arbitrary network of pores. We propose novel boundary conditions and interpret the model using a transmission line circuit approach, specifically for the electrochemical potential of charge – the valence-weighted sum of ionic electrochemical potentials. This innovative methodology unveils the effective Kirchhoff's laws in the network and demonstrates excellent agreement with direct numerical simulations while offering computational speeds that are significantly faster. Leveraging the derived model, we investigate the effects of pore arrangement and polydispersity on given pore-size distributions. Our analysis reveals valuable insights into how different pore configurations can influence the performance of energy storage devices. |
Sunday, November 19, 2023 9:31AM - 9:44AM |
A32.00008: Asymptotic solutions for the electric potential and complex impedance of disc electrodes in high-conductivity electrolyte solutions Kenneth Yamamoto, Anil Koklu, Ali Beskok, Vladimir S Ajaev The study of electrical double layers near charged surfaces in electrolyte solutions is crucial for a range of applications, such as biophysics, colloidal science, and micro/nanofluidics. We derive asymptotic formulas for the electric potential and complex impedance of polarized disc electrodes in an electrolyte solution subject to a small external AC voltage based on the Debye–Falkenhagen approximation to the coupled Poisson–Nernst–Planck equations. Results from asymptotic formulas for the complex impedance are compared with experimental data, and scales for impedance and frequency are identified that lead to self-similar behavior. This analytical modeling can aid in optimizing electrode design and inform the use of dielectrophoresis techniques for manipulating and characterizing biological analytes in microfluidic devices. |
Sunday, November 19, 2023 9:44AM - 9:57AM |
A32.00009: Molecular Investigations of the Electroosmotic Transport in Nanochannels Grafted with Cationic Polymer Chains Siddhartha Das, Raashiq Ishraaq, Tanmay S Akash Liquid transport in nanochannels can be significantly influenced by grafting the nanochannel walls with environmental-stimuli-sensitive polymer chains. In this study, we employ all-atom molecular dynamics (MD) simulations to study the electroosmotic (EOS) water transport in nanochannels grafted cationic polyelectrolyte (PE) chains, namely PMETA [Poly[(2-(Methacryloyloxy)Ethyl) Trimethylammonium] chains, screened with chloride counterions. Our previous study has demonstrated the most remarkable coion-driven EOS transport and reversal of the direction of the EOS flow field via alteration of the electric field strengths in nanochannels grafted with sodium-counterion-screened anionic PE chians (polyacrylic acid or PAA chains). In this present study, we shall probe the possibility of such coion-driven EOS flow and the effect of cationic PE chain charges and the nature of the screening counterions on the resulting EOS flow. These findings will be specially interesting given our recent discovery of significantly large cholride counterion mobility inside the PMETA PE layer owing to the locally hydrophobic nature of the PMETA chains. This enhanced mobility of the chloride counterions inside the PMETA PE layer is several times more than the sodium counterion mobility inside the grafted anionic PAA layer, and hence is expected to significantly influence the overall nanochannel EOS flows. |
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