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 L13: Electrokinetic Flows: Modulations |
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Chair: Jesse Ault, Brown University Room: 140 |
Monday, November 21, 2022 8:00AM - 8:13AM |
L13.00001: Time-varying solute strategies to maximize diffusiophoretic extraction from confined geometries Jesse T Ault Diffusiophoresis has emerged as an excellent candidate for driving the targeted motion of colloidal particles in confined systems. For example, recent research on diffusiophoresis in dead-end pores has shown that exposing a pore to a nearly-discontinuous solute concentration can generate a powerful diffusiophoretic transport of suspended particles that can greatly enhance their motion by orders-of-magnitude beyond simple Brownian motion, which has applications for problems such as particle injection and withdrawal. Here, we consider the efficiency of such a process, both for the case of injection and withdrawal. For example, in the case of withdrawal, a certain fraction of the particles initially occupying the pore can be predicted to be extracted throughout this diffusiophoretic cycle. This efficiency will be a function of the diffusiophoretic mobility, solute diffusivity, length of the pore, and the solute contrast ratio that drives the dynamics. Finally, we show how a modified, time-varying diffusiophoresis strategy can be used to increase the efficiency of these injection and withdrawal processes. This work has applications from targeted drug delivery to enhanced oil recovery. |
Monday, November 21, 2022 8:13AM - 8:26AM |
L13.00002: Geometrical modulation of electrokinetic streaming potential when electrolyte flows over liquid-filled surfaces Bei Fan, Prabhakar R Bandaru Electrokinetic flow, which can generate electrical voltage through the flow of an electrolyte over a charged surface, may be used for energy transduction. However, the yielded low streaming potential of electrokinetic flow on flat surface limited its practical applications. We have found that enhanced streaming potential could be obtained through the flow of salt water on liquid-filled surfaces that are infiltrated with a lower dielectric constant liquid, such as oil, to harness both of the electrolyte slip and associated surface charges. The geometrical factors of liquid-filled surfaces will influence the effective zeta potential of liquid-filled surface through influencing the fluid slip and contribution of liquid-oil interface to zeta potential. The geometrical factors can be well controlled during the slippery liquid-filled surface fabrication process. Thus, there is a large space of control parameters in modulating streaming potential, and it is important to study the effects of these geometrical parameters on streaming potential. Then the new obtained knowledge will be useful to optimize the geometry of liquid-filled surface for substantial streaming potential or streaming current generation. We have systematically investigated the effects of groove depth, groove width and groove fraction on streaming potential experimentally. Besides, we also derived the theoretical effective channel zeta potential. And a good comparison between the experimental results and theoretical channel zeta potential was found. These results lay the basis for innovative surface charge engineering methodology for the study of electrokinetic phenomena at the microscale, with possible application in new electrical power sources, and yield insights into understanding geometrical effects in electrolyte flows with implications to the establishment of local electric fields, energy generation, and biological separations. |
Monday, November 21, 2022 8:26AM - 8:39AM |
L13.00003: The contributions of hydrodynamics and surface charge to the electrical conductivity of nanochannels Aref Hashemi, Raul P Pelaez, Aleksandar Donev We use Brownian Dynamics to investigate the induced ionic current and electro-osmotic flow in a slit channel by an external electric field. The individual ions are modeled as Brownian particles with Gaussian charges, and interact with each other and the walls of the channel electrostatically, hydrodynamically, and via a steric Lennard-Jones like potential. Our spectral numerical method solves the Stokes equations for the fluid flow together with the Poisson equation for electrostatics to compute the dynamics of the particles. We analyze how the surface charge of the channel walls and electrohydrodynamic flows affect the conductivity of the confined electrolyte solution. |
Monday, November 21, 2022 8:39AM - 8:52AM |
L13.00004: Convection rolls and 3D particle dynamics in merging solute streams Robben Migacz, Guillaume Durey, Jesse T Ault Microparticles migrate in response to gradients in solute concentration through diffusiophoresis and diffusioosmosis. Merging parallel streams of fluid with distinct solute concentrations is a common strategy for producing a concentration gradient in microfluidic devices; the gradient is then (approximately) perpendicular to the flow and results in the transverse migration of particles. This is particularly useful in separation and filtration processes, as it results in regions of particle accrual and depletion in continuous flows. This has been examined in several classic papers on diffusiophoresis, but previous works do not comment on particle dynamics near walls of nonzero surface charge, which we find to be distinct from the dynamics in the bulk. We show, through experiments and simulations, that diffusioosmotic flow along certain boundaries can result in significant particle focusing in near-wall regions. The "convection rolls," which draw plain polystyrene particles away from regions of high solute concentration close to walls, are apparent in the inlet region near a glass surface but vanish when the surface is plated with gold (a conductor). This could have implications for the fabrication of microfluidic devices for applications of diffusiophoresis. |
Monday, November 21, 2022 8:52AM - 9:05AM |
L13.00005: Suppression of electroconvection due to van der Waals attraction of polymers dissolved in an electrolyte towards a metal electrode Ankush Mukherjee, Lynden Archer, Donald L Koch Electroconvection enhances non-planar deposition on the surface of electrodes and reduces the life of batteries. Polymers with modest molecular weights dissolved in the bulk electrolyte are attracted to the metal electrode due to weak van der Waals forces of attraction. This results in a thin (order 10-100 nm) layer with a higher concentration of dissolved polymers near the ion-selective surface. The van der Waals force acting on the polymers acts as a restoring body force that opposes the growth of incipient convective motions. Using linear stability analysis and numerical simulations, we show that this restoring body force increases the critical voltage for the onset of electroconvection and reduces the growth rate of electroconvective modes above the critical voltage. Analysis of quartz crystal microbalance (QCM) experimental results confirms the presence of a polymer layer near the metal electrode. The variation of the time required for the onset of significant electroconvective motions as a function of applied voltage in experiments is compared to the variation predicted by our analysis. |
Monday, November 21, 2022 9:05AM - 9:18AM |
L13.00006: Electrohydrodynamics and Rheology: Direct Ink Writing of Highly Conducting PEDOT:PSS-Based Polymer Blends jevon plog, Xinnian Wang, Ketki Lichade, yayue pan, Alexander L Yarin Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) is a conducting polymer that holds great promise for electronic applications. This study proposes effective methods for enhancing the electrical conductivity and, simultaneously, the printability of inks containing PEDOT:PSS. Direct Ink Writing (DIW) imposes strict requirements on the rheological properties of the printed inks, thus limiting the choice of qualifying materials. To improve the printing processability, countless materials have been added to pristine PEDOT:PSS in the past, but do so at the expense of the electrical conductivity. The present work develops PEDOT:PSS-based polymer blends capable of enhancing the electrical conductivities while concurrently meeting the demanding requirements of extrusion-based additive manufacturing. In addition to an increased electrical conductivity from polymer doping, it is demonstrated that a post-processing humidity treatment further increases the electrical conductivity. Moreover, the electrostatically-assisted direct ink writing (eDIW), a novel extrusion-based additive manufacturing technique introduced here, revealed that it is capable of creating electrically conductive 2D and 3D circuits at an increased printing speed and at a higher resolution. |
Monday, November 21, 2022 9:18AM - 9:31AM |
L13.00007: Diffusioosmotic dispersion in a long, narrow channel Jian Teng, Bhargav Rallabandi, Jesse T Ault Solute-surface interactions have garnered considerable interest in recent years as a novel control mechanism for driving unique fluid dynamics transport with potential applications to fields such as biomedicine, the development of microfluidic devices, and enhanced oil recovery. In this study, we will discuss dispersion induced by the diffusioosmotic motion near a charged wall in the presence of a solute concentration gradient. Here, we introduce a Gaussian plug of salt at the center of a channel with no background flow. The gradient in solute concentration drives a diffusioosmotic slip flow at the walls, which results in a recirculating flow in the channel; this, in turn, drives an advective flux of the solute concentration. This effect introduces cross-stream diffusion of the solute, altering the effective diffusivity. We will present theoretical predictions for the solute dynamics using a multiple-timescale analysis to quantify the dispersion driven by the solute-surface interactions. In addition, we will present numerical simulations to validate our theoretical predictions. Finally, we will comment on the effective diffusivity and long-time dynamics. |
Monday, November 21, 2022 9:31AM - 9:44AM |
L13.00008: Shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids Sangwoo Shin, Viet Sang Doan, Dong-Ook Kim, Craig Snoeyink, Ying Sun We present diffusiophoresis of ellipsoidal particles induced by ionic solute gradients. Unlike the common belief that diffusiophoresis is shape-independent, here we show that this assumption breaks down when the thin Debye layer approximation is relaxed. Using particle tracking microscopy, we find that the diffusiophoretic mobility of ellipsoids is sensitive to the eccentricity and the orientation of the ellipsoid relative to the imposed solute gradient. We show that such shape- and orientation-dependent diffusiophoresis of colloidal ellipsoids can be easily captured by modifying previous theories for spheres. |
Monday, November 21, 2022 9:44AM - 9:57AM Author not Attending |
L13.00009: Automated device for multi-stage paper-based assays enabled by an electroosmotic pumping valve Baruch Rofman, Rawi Naddaf, Maya Bar-Dolev, Tal Gefen, Naama Geva-Zatorsky, Moran Bercovici We leverage electroosmotic flow generation in porous media in combination with a hydrophobic air gap to create a controllable valve capable of operating in either finite dosing or continuous flow mode, enabling the implementation of multi-step assays on paper-based devices. The hydrophobic air gap between two paper pads creates a barrier keeping the valve nominally closed. Electroosmotic actuation, implemented using a simple pair of electrodes under the upstream pad, generates sufficient pressure to overcome the barrier and connect the two pads. We present a model describing the flow and governing parameters, including the critical electric potentials required to open and close the valve and the threshold potential for switching between the modes of operation. We construct the valve's air gap using a hierarchical superhydrophobic surface and study the stability of the closed valve under strenuous conditions and find a good agreement between our model and experimental results, as well as stable working conditions for practical applications. We present a straightforward design for a compact and fully automated device based on paper pads placed on top of simple printed circuit boards, equipped with heating and actuation electrodes and additional power and logic capabilities. Finally, we demonstrate the use of the device for amplification of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) sequences directly from raw saliva samples, using a Loop-mediated isothermal amplification (LAMP) protocol requiring sample lysis followed by enzymatic deactivation and delivery to multiple amplification sites. Since printed circuit board (PCB) costs scale favorably with mass production, we believe that this approach could lead to a low-cost diagnostic device that offers the sensitivity of amplification methods. |
Monday, November 21, 2022 9:57AM - 10:10AM |
L13.00010: Charge-Wettability interaction in a Graphene-based nanopore modulating DNA translocation. Avinash Kumar, Chirodeep Bakli Translocation of DNA through nanopores under an externally applied electric field for characterization of constituent nucleotides is under intensive research. The major challenge is to control the speed of DNA so that the sensor can catch the variation in the ionic current and can read the individual bases. Researchers have used protein-based biological nanopores which are replaced by solid-state nanopores (SS-NP) because of its benefit of controlled size, surface charge, and surface finishing over biological nanopores. Hence, SS-NP is being potentially used as a rapid DNA sequencing device. However, the thickness of the nanopores fabricated in insulating membranes is equivalent to 15-20 bases thereby, making it difficult to detect each nucleotide. With the advent of 2-D materials, graphene-based membranes with a single atomic thickness (0.34 nm) can be potentially used as a sensor to obtain single-base resolution in the ionic current variation. Towards this here we present full-scale mathematical modelling of DNA translocation through a graphene-based membrane. We consider the coupling of the interfacial interaction of graphene substrate with charge and momentum transport to predict the modified electro-hydrodynamics of the DNA nanoparticle. We include a separate dielectric permittivity of the graphene membrane with a varying surface charge to consider its effect on DNA dynamics in the present model. The present study explores regimes of successful or failed translocation of DNA through graphene-based nanopores with comparatively lower computational costs, unlike typical molecular dynamics simulations. |
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