Bulletin of the American Physical Society
76th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 19–21, 2023; Washington, DC
Session J34: Micro/Nano scale Flows: Electrokinetics |
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Chair: Ankur Gupta, University of Colorado, Boulder Room: 201 |
Sunday, November 19, 2023 4:35PM - 4:48PM |
J34.00001: Does electrophoretic velocity depend on particle size in viscoelastic fluids? Joseph Bentor, Xiangchun Xuan In theory, electrophoretic velocity is independent of particle size in an unbounded Newtonian fluid under the thin electric double layer approximation. However, recent theoretical studies have challenged this notion, revealing that the electrophoretic velocity may exhibit a dependency on particle size in non-Newtonian fluids. We report a systematic experimental study of this phenomenon in viscoelastic polyethylene oxide (PEO) solutions through a rectangular microchannel. By manipulating the molecular weight as well as the concentration of PEO polymer, we aim to examine the individual and combined influences of fluid viscoelasticity and shear thinning at different levels on the electrophoretic velocity of spherical particles with (nearly) identical zeta potentials (in a Newtonian fluid) but of different diameters. Our findings indicate a significant amplification of the difference in electrophoretic velocity across various particle sizes with increasing polymer molecular weight and polymer concentration. |
Sunday, November 19, 2023 4:48PM - 5:01PM |
J34.00002: Effects of fluid shear-thinning on electrokinetic instability in microchannel flows with conductivity gradients TO-LIN Chen, Rajguru Boobalan, Isaiah Glenn, Seyedmojtaba Tabarhoseini, Mahmud Raihan, Lung-Ming Fu, Xiangchun Xuan Electrokinetic instability (EKI) arises from the action of electric field on fluid flow with conductivity gradients. It has been extensively studied in Newtonian fluids for the applications of, for example, micromixing and sample stacking. However, very little is known regarding EKI in non-Newtonian fluids. We present in this work a fundamental study of EKI in shear-thinning xanthan gum (XG) solutions through a T-shaped microchannel. The concentration of XG polymer is varied from 0 ppm (corresponding to the case of a Newtonian fluid) to 3000 ppm for the purpose of achieving a range of fluid shear-thinning effects. We examine how the electrokinetic flow pattern of XG solutions develops with the imposed electric field and differs from that of a Newtonian fluid. We also study how the change of XG concentration affects the threshold electric field for the onset of EKI. |
Sunday, November 19, 2023 5:01PM - 5:14PM |
J34.00003: On the Competing Effects of Buoyancy-Driven and Electrothermal Flows in Microchannels Ali Beskok, Mohammad K Manshadi Ionic fluids subjected to externally applied electric fields experience Joule heating, which increases with the increased electric field and ionic conductivity of the medium. Temperature gradients induced by Joule heating can create buoyancy-driven flows produced by local density changes, as well as electrothermal transport due to the temperature-dependent variations in fluid permittivity and conductivity. Here we consider Joule heating induced transport in microchannels by a pair of electrodes under alternating current electric fields. Resulting buoyancy-driven and alternating current electrothermal (ACET) flows are investigated theoretically, numerically and experimentally. Proper normalizations of the governing equations led to the ratio of the electrothermal and buoyancy velocities, as a new non-dimensional parameter, which enabled the construction of a phase diagram that can predict the dominance of ACET and buoyancy-driven flows as a function of the channel size and electric field. Numerical results were used to verify the phase diagram in various height microchannels for different ionic conductivity fluids and electric fields, while the numerical results were validated using the micro-particle-image velocimetry technique. The results show that ACET flow prevails when the channel dimensions are small, and the electric potentials are high, whereas buoyancy-driven flow becomes dominant for larger channel heights. The present study brings insights into Joule heating-induced transport phenomena in microfluidic devices and provides a pathway for the design and utilization of ACET-based devices by properly considering the co-occurring buoyancy-driven flow. For details see: doi:10.1017/flo.2023.19. |
Sunday, November 19, 2023 5:14PM - 5:27PM |
J34.00004: Enhanced transport of Li+ over other alkali ions in small-diameter carbon nanotubes Da-Chi N Yang, Richard J Castellano, Ricardo P Silvy, Robert F Praino, Francesco Fornasiero, Jerry W Shan Ion transport in angstrom-scale 1-D pores is of interest to understanding biological channels, as well as for applications in separation membranes. In such confined pores, hydrated ions undergo partial or complete dehydration, where water molecules around the ions are reoriented or stripped away in order to enter the pores. Here, we describe experiments comparing the pressure- and electric-field- driven transport of various alkali ions in 0.8-nm and 3-nm carbon-nanotube CNT pores. In both types of nanotubes, the transport is selective to cations due to positively charged functional groups at the nanotube tips. However, in 0.8-nm pores, both the pressure-driven streaming current and the ionic conductance are greater for Li+ ions than for K+ ions, which is a reversal of their relative mobilities in bulk solution. The enhanced transport of Li+ over other alkali ions is consistent in 0.8-nm CNT pores regardless of the concentration of the alkali metal chloride solutions. In contrast, for 3-nm CNTs pores, the faster relative transport of Li+ compared to K+ only occurs below a certain concentration, and reverses at higher concentrations. We attribute this behaviour to the varying thickness of the electric double layer as compared to the pore diameter. Better fundamental understanding of the complex interactions between ions and 1-D nanopores may enable rational design of membranes for lithium recovery, desalination, and other separation applications. |
Sunday, November 19, 2023 5:27PM - 5:40PM |
J34.00005: Diffusiophoresis-Enhanced Turing Patterns Benjamin Alessio, Ankur Gupta Turing patterns are essential in biophysics, emerging from short-range activation and long-range inhibition processes in reaction-diffusion systems. However, their paradigm is based on diffusive transport processes, which yields Turing patterns that are less sharp than the ones observed in nature. A complete physical description of why the Turing patterns observed in nature are significantly sharper than state-of-the-art models remains unknown. Here, we propose a novel solution to this phenomenon by investigating the role of diffusiophoresis in Turing patterns. The inclusion of diffusiophoresis enables one to generate patterns of colloidal particles with significantly finer length scales than the accompanying chemical patterns. Further, diffusiophoresis enables a degree of control that allows for robust modeling of fish patterns which would otherwise require ad hoc techniques. We present a scaling analysis indicating that chromatophores, ubiquitous in biological pattern formation, are likely diffusiophoretic, and that their Péclet number controls the pattern enhancement. Our theoretical results are strongly supported by the recent experiments on diffusiophoretic pattern formation and sharpening of biomolecules in the MinDE protein system of extit{E. coli} and we illustrate qualitative agreement between the two. This discovery suggests important features of biological pattern formation can be explained with a universal mechanism that is quantified straightforwardly from the fundamental physics of colloids and inspires future exploration of adaptive materials, lab-on-a-chip devices, and tumorigenesis. Alessio and Gupta (2023): arXiv:2305.11372 |
Sunday, November 19, 2023 5:40PM - 5:53PM |
J34.00006: Maximizing diffusiophoretic extraction from confined geometries using time-varying solute strategies Morgan Castleberry, Morgan Castleberry, Robben Migacz, Jesse T Ault This work explores the impact of solute concentration at the boundary of a domain on the gradient-induced motion of colloidal particles. This phenomenon, known as diffusiophoresis, has the potential to improve efficiency of particle motion through confined geometry by orders of magnitude over that of simple Brownian motion. For example, previous research has found that near-discontinuous solute concentration at the boundary of a pore can lead to significantly enhanced efficiency of motion. We expand upon that finding, using both simulations and experiments, to understand more complex boundary conditions. In particular, we test singular and pulsing near-discontinuities in the solute gradient, and compare the resulting efficiencies of their induced motion. We conclude that these modified conditions can further strengthen the diffusiophoretic motion, and therefore the efficiency of injection and withdrawal processes. This could lead to great enhancements of such processes as oil recovery or targeted drug delivery. |
Sunday, November 19, 2023 5:53PM - 6:06PM |
J34.00007: Phoretic Transport of Colloids through Solute-loaded Hydrogel Lattices Zehao Chen, Mobin Alipour, Amir Pahlavan Hydrogels can be loaded and then gradually release solutes on demand, a feature that has proven useful in the context of drug delivery applications. Here, we report on how the interplay between flow and localized solute gradients formed around a hydrogel array influences the transport, clustering, and dispersion of colloidal particles. We finally discuss the potential implications of our observations for applications such as separation and filtration, colloid transport in dissolving porous media and targeted drug delivery to cancer cells. |
Sunday, November 19, 2023 6:06PM - 6:19PM Author not Attending |
J34.00008: Abstract Withdrawn
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Sunday, November 19, 2023 6:19PM - 6:32PM |
J34.00009: Disorder-mediated diffusiophoretic transport of colloids Aditya Pujari, Haoyu Liu, Mobin Alipour, Amir Pahlavan Diffusiophoresis is the spontaneous motion of colloidal particles under the influence of a solute concentration gradient. When a solute front is introduced in a porous media laden with colloidal particles, diffusiophoresis is prevalent on the local pore-scale. Our observations indicate that despite its transient nature, diffusiophoretic migration manifests in the macroscopic transport of the colloid. Here, we report on the influence of medium disorder on the coupled transport and dispersion of colloids and solute using microfluidic experiments and numerical simulations. |
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