Bulletin of the American Physical Society
75th Annual Meeting of the Division of Fluid Dynamics
Volume 67, Number 19
Sunday–Tuesday, November 20–22, 2022; Indiana Convention Center, Indianapolis, Indiana.
Session Z13: Electrokinetic Flows: Interfaces & Nano |
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Chair: Sangwoo Shin, University of Buffalo Room: 140 |
Tuesday, November 22, 2022 12:50PM - 1:03PM |
Z13.00001: Electrical-Double-Layer Charging in a Complex Network of Pores Filipe H Henrique, Ankur Gupta, Pawel J Zuk Ion transport in charged porous media plays a pivotal role in applications ranging from capacitive deionization to electrochemical capacitors. Three factors affect transport: double-layer thickness, ionic properties (valences and diffusivities), and the geometry of the porous network. While experimental reports suggest that the porous-network geometry dictates the transport of ionic species, modeling approaches that can predict such dependencies are scarce due to the complexity of the porous geometry and the coupled nature of governing equations. |
Tuesday, November 22, 2022 1:03PM - 1:16PM |
Z13.00002: Dynamics of Multicomponent Electrolyte Transport Including the Effects of Electrical Double Layers and Redox Reactions Nathan Jarvey, Filipe Henrique, Ankur Gupta
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Tuesday, November 22, 2022 1:16PM - 1:29PM |
Z13.00003: Polarization of disc and ring electrodes in high-conductivity electrolyte solutions Kenneth Yamamoto, Anıl Köklü, Ali Beskok, Vladimir S Ajaev Studies of electrical double layers near charged surfaces in electrolyte solutions are important for a wide range of applications including biophysics, colloidal science, and micro/nanofluidics. We investigate the polarization of disc and ring electrodes immersed in an electrolyte solution and subjected to a small external AC voltage governed by the Debye−Falkenhagen equation (a linearization of the Nernst−Planck equations) and the Poisson equation. Based on integral transforms, analytical techniques are developed for predicting the space charge density and complex impedance of the system. The effect of electrode dimension on the impedance is examined and compared with experiments. These mathematical models enable uncovering detailed knowledge of the surface charge densities on the electrodes from experimental impedance spectroscopy measurements. |
Tuesday, November 22, 2022 1:29PM - 1:42PM |
Z13.00004: A Fourier-Chebyshev non-interpolating method for the direct numerical simulation of two-dimensional wall-induced electrokinetic flow Philipp G Marthaler, Andreas G Class Transport of samples in microfluidic systems relies on electrokinetic pumps or actuators. The working principle of these actuators is induced charge electroosmosis. The traditional approach to predict the behavior of such systems utilizes the Smoluchowski slip condition. Thus, the Poisson-Nernst-Planck system can be solved separately from the flow using the boundary conditions for coupling. |
Tuesday, November 22, 2022 1:42PM - 1:55PM |
Z13.00005: Self-organized Vortex Structures of Three-dimensional Electroconvection in a Confined Geometry Yeonuk Yu, Sunghoon Kim, Van Sang Pham, Rhokyun Kwak Here, we describe the first laboratory visualization of 3D Electroconvection (EC; a hydrodynamic instability) in confined geometries, a scenario often found in many electrochemical systems with internal flows bounded in narrow channels. Combining experiment and numerical modeling in a confined structure composed of identical ion exchange membranes at the top and bottom and a non-permeable polygonal sidewall, we figured out that the vortex boundary of EC is always formed perpendicular to the sidewall to minimize frictional energy loss. If this wall effect becomes dominant as the aspect ratio of the channel decreases and/or the voltage increases, we observed a self-organized vortex structure by converging the vortices from the sidewalls at the center of the channel. In this condition, the number of vertices of the confined wall determines the number of self-organized vortices; e.g., 3 vortices in a triangular channel. When we contained the EC in a circular channel with an infinite number of vertices, the number of self-organized vortices can be adjusted with respect to the applied voltage. On the other hand, if the aspect ratio increases and/or voltage decreases, a group of polygonal vortex patterns was developed, and a few vortices on the sidewall have a perpendicular boundary. |
Tuesday, November 22, 2022 1:55PM - 2:08PM |
Z13.00006: Electroconvection in the Presence of PEG Oligomer Additives Arpita Sharma, Lynden Archer, Donald L Koch Metal electrodeposition in batteries is fundamentally unstable and affected by different instabilities depending on operating conditions and chemical composition. Particularly at high charging rates, a hydrodynamic instability called electroconvection sets in that aggravates the situation by creating non-uniform ion flux and preferential deposition at the electrode. In this talk, I will discuss our experimental work focusing on how PEG oligomer additives interact with electroconvective flow at a cation selective interface. By combining electrochemical characterization techniques and direct visualization experiments, we found that electroconvection is delayed and suppressed at all voltage in the presence of oligomers. Our results also reveal that it is important to consider the role of polymers at the interface, in addition to their bulk effects, to understand the stabilization effect and its mechanism. To this end, I will also discuss a theoretical polymer layer model we developed to corroborate our experimental results and explore the possible physics behind the increased stability and its eventual saturation. |
Tuesday, November 22, 2022 2:08PM - 2:21PM |
Z13.00007: Electroconvective Viscous Fingering in a Polyelectrolyte solution on a Charge Selective Surface Jeonghwan Kim, Joonhyeon Kim, Rhokyun Kwak Viscous fingering is one of the most widely observed phenomenon of interfacial instabilities, which occurs at the interfaces of two fluids when a low viscous fluid displaces a highly viscous one. Despite its generality in Nature and engineering applications, viscous fingering has rarely been observed in a single fluid system. In this study, we describe the first observation of viscous fingering within a single polyelectrolyte solution on a charge selective surface. The fingering in a single fluid is realized by developing of ion concentration polarization and electroconvection (EC) on an ion exchange membrane, via applying an external electric field. Combining experiment and scaling analysis, we successfully described the onset and pattern of this electroconvective viscous fingering according to RaE (electric Rayleigh number), M (viscosity ratio) and Sc (Schmidt number), including (i) transition of the conventional to finger-like EC and (ii) transition of a single finger pattern to ramified one. Also, we investigate that the number of single and ramified fingers has a single curve relation with RaE, which is comparable to the relation of the conventional viscous fingering between the finger width and Ca (capillary number) despite in the zero interfacial tension limit. |
Tuesday, November 22, 2022 2:21PM - 2:34PM |
Z13.00008: Electrical Circuit Modelling of Nanofluidic Systems John Sebastian, Yoav Green In this talk, we will address one of the central challenges faced by the nanofluidics community: scaling the electrical properties of a single nanochannel to that of a nanoporous membrane. We demonstrate that the electrical circuit of an array of nanochannels and microchannels is equivalent to a parallel circuit of mutually independent single-channel systems [1], comprised of three serially connected resistance contributions: the microchannel and nanochannel resistances and the field-focusing resistance. Field-focusing resistances are a generalization to the classical access resistance solution (limited to highly isolated circular pores) and hold for interacting pores of any geometry. Notably, the total resistance of the array is shown to scale inversely with the number of channels. Our approach provides an invaluable tool for analyzing and interpreting experimental measurements, characterizing surface charge properties of newly developed materials, and a method for the design and development of function-specific nanofluidic devices. |
Tuesday, November 22, 2022 2:34PM - 2:47PM |
Z13.00009: Real-time feedback control for engineered nanoelectrokinetic preconcentrator Taewan Kim, Sungjae Ha, Sung Jae Kim Nanoelectrokinetic preconcentration using ion concentration polarization (ICP) phenomenon is a highly effective method for simultaneously separating and concentrating biomolecules. Hence, this approach has been widely adopted in diagnostic applications, in which the presence of low abundant target is detected in a microfluidic channel. |
Tuesday, November 22, 2022 2:47PM - 3:00PM |
Z13.00010: Nanoparticle Enrichment by the reversal AC Electroosmotic Flow Ahmed Abdelghany, Takumi Matsushima, Yoshiyasu Ichikawa, Masahiro Motosuke Microfluidic devices provide advantages such as rapid reactions, portability, less sample volume, and the availability of on-chip multi-functional integration. A particle control in the microfluidic platform often brings beneficial effects for improved performance of the device or highly sensitive analysis. This study demonstrates a novel approach for nanoparticle enrichment driven by the reversal alternating current electroosmotic flow (rACEO). The process of nanoparticle enrichment in a microfluidic device embedded with a coplanar symmetric electrode array was examined. Nanoparticles in a solution were driven by rACEO to be concentrated into the electrode's gap at a high-frequency range of AC signal, typically 50-150 kHz. We could achieve over tenfold rise in the concentration of polystyrene particles having a diameter of 100 nm from the initial concentration. This result demonstrates a potential application of rACEO for focusing rare species in the sample in the way to enhance the detection sensitivity. |
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