Bulletin of the American Physical Society
71st Annual Meeting of the APS Division of Fluid Dynamics
Volume 63, Number 13
Sunday–Tuesday, November 18–20, 2018; Atlanta, Georgia
Session M24: Microscale Flows: Phoretic Effects |
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Chair: Federico Toschi, Eindhoven University of Technology Room: Georgia World Congress Center B312 |
Tuesday, November 20, 2018 8:00AM - 8:13AM |
M24.00001: CO2 driven diffusiophoresis and water cleaning: similarity solutions for predicting the exclusion zone in a channel flow Suin Shim, Mrudhula Baskaran, Howard A. Stone We investigate diffusiophoretic separation of negatively charged particles in a rectangular channel flow, driven by CO2 dissolution from one wall. Since the negatively charged particles create an exclusion zone near the boundary where CO2 is introduced, we model the problem by applying a shear flow approximation in a 2D configuration. From the form of the equations we define a similarity variable to transform the reaction-diffusion equations and particle distribution equations to ODEs. The definition of the similarity variable suggests a characteristic length scale for the particle exclusion zone. We consider height-averaged and different orientation of the flow behaviors in rectangular channels to rationalize and connect our experimental observations with the model. Our observations and the theoretical model provide design parameters such as flow rate, channel dimensions and CO2 pressure for the in-flow water cleaning systems. |
Tuesday, November 20, 2018 8:13AM - 8:26AM |
M24.00002: Boosting CO2-driven diffusiophoresis of colloidal suspensions by permeation Orest Shardt, Sangwoo Shin When carbon dioxide dissolves into an aqueous colloidal suspension, the resulting transient pH gradients drive diffusiophoresis of the suspended particles. We investigate the effects of CO2 permeation on the extent of particle motion in a model system consisting of a suspension-filled pore in a gas-permeable polymer. Pure CO2 is applied to both ends of the pore and the outer surface of the polymer is either sealed (preventing steady leakage of CO2) or open to the atmosphere, in which case a steady CO2 (and pH) distribution is established. For both cases, we compute the transient CO2 distributions (in the water and polymer) and the diffusiophoretic migration of suspended particles. For the second (open) case, we also determine the steady particle distribution. Loss of CO2 into the surrounding material increases the magnitude and duration of the pH gradient and therefore boosts the migration of the particles. We evaluate the effects of the thickness of the polymer around the pore and the permeability of the polymer to CO2 (the product of the solubility and diffusivity of CO2 in the polymer). An optimal diffusivity maximizes the displacement of the particles. The numerical predictions are consistent with experiments in poly(dimethylsiloxane) blocks with varying thicknesses. |
Tuesday, November 20, 2018 8:26AM - 8:39AM |
M24.00003: The Effect of Electrolyte on Diffusiophoresis in One-Dimensional Salt Gradients Jessica L. Wilson, Suin Shim, Ankur Gupta, Howard A Stone We study the diffusiophoretic motion of negatively charged particles in one dimensional salt gradients using a dead-end pore geometry and various salt solutions. We estimate the diffusiophoretic velocities for particles for a range of background electrolytes such as multi-valent and asymmetric (non-z:z) electrolytes. Theoretical investigations of asymmetric electrolyte diffusiophoresis support our findings that the choice of electrolyte significantly influences the movement of particles, and in particular the chemiphoretic component of the diffusiophoretic velocity. By combining theoretical and experimental analysis, we present the relative importance of electrophoretic and chemiphoretic contributions in electrolyte solutions. |
Tuesday, November 20, 2018 8:39AM - 8:52AM |
M24.00004: Colloidal accumulation in flow junctions induced by fluid flow and dissolved solutes Sangwoo Shin, Jesse T Ault, Patrick B Warren, Howard A Stone The flow of solutions containing solutes and colloidal particles in porous media is widely found in systems including underground aquifers, hydraulic fractures, estuarine or coastal habitats, water filtration systems, etc. In such systems, solute gradients occur when there is a local change in the solute concentration. While the effects of solute gradients have been found to be important for many applications, we observe an unexpected colloidal behavior in porous media driven by the combination of solute gradients and the fluid flow. When two flows with different solute concentrations are in contact near a junction, a sharp solute gradient is formed at the interface, which may allow strong diffusiophoresis of the particles directed against the flow. Consequently, the particles accumulate near the pore entrance, rapidly approaching the packing limit. These colloidal dynamics have important implications for the clogging of a porous medium, where particles that are orders of magnitude smaller than the pore width can accumulate and block the pores within a short period of time. |
Tuesday, November 20, 2018 8:52AM - 9:05AM |
M24.00005: Diffusiophoresis in a Weakly Viscoelastic Fluid Shabab Saad, Giovanniantonio Natale Self-propelling active colloids (AC) provide insights in the behavior of non-equilibrium systems by producing enhanced diffusive motion. Our model system consists of synthetic Janus (Pt/Si) microspheres undergoing diffusiophoresis (via local concentration gradient) in presence of H2O2. In this study, we aim to address for the first time the single-particle dynamics in a weakly viscoelastic fluid. Experimentally, Janus particles were dispersed in dilute PVP water solutions. The solution presented Newtonian shear viscosity with a finite but relatively short (~3ms) relaxation time. The Deborah number, based on the motion of the particles, was calculated to be in the order of 10-4. Within this regime, we attempt to investigate the coupling between the solute concentration field and the phoretic particle's motility (MSD, velocity and diffusivity analyzed via MPT) because of the weak viscoelastic medium. These findings are the foundations to understand collective motion of ACs in complex media and to study the interplay between particle organization [1] and fuel concentration in the limit of low Péclet number. Since any biological fluid is a viscoelastic fluid, the characterization of swimming dynamics is of high relevance for potential drug delivery applications.
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Tuesday, November 20, 2018 9:05AM - 9:18AM |
M24.00006: Abstract Withdrawn
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Tuesday, November 20, 2018 9:18AM - 9:31AM |
M24.00007: On-chip microscale thermophoresis using MEMS-fabricated fluidic channel Tetsuro Tsuji, Satoyuki Kawano A temperature difference in microscale spatial distance in fluid can produce a strong temperature gradient, which induces thermophoresis of dispersed micro/nano particles. Such a particle transport, microscale thermophoresis, is expected to develop a new particle manipulation technique used in micro- and nanofluidic devices, since it has different physical characteristics from common methods such as electrophoresis. In the present study, we fabricate a microfluidic device with a micro heater using micro-electro-mechanical systems (MEMS) technologies and demonstrate that the microscale thermophoresis effectively controls the flow of microparticles. In particular, we find that polystyrene and silica microparticles have opposite responses to the temperature gradient, realizing the selective particle transport in the microfluidic system. |
Tuesday, November 20, 2018 9:31AM - 9:44AM |
M24.00008: Hydrodynamic fluctuations in quasi-two dimensional diffusion Florencio Balboa Usabiaga, Raúl P Peláez, Sergio Panzuela, Qiyu Xiao, Rafael Delgado-Buscalioni, Aleksandar Donev A common feature of many biological systems is the diffusion of particles in a two-dimensional interface immersed in a three-dimensional fluid. Think for example of proteins diffusing in a lipid membrane. It is known that in these systems the interplay between hydrodynamic interactions and Brownian fluctuations leads to anomalous diffusion, in which the collective diffusion coefficient diverges like the inverse of the wavenumber. Here, we use particle simulations and fluctuating hydrodynamics to study the diffusion of colloids in a simplified system, ideal |
Tuesday, November 20, 2018 9:44AM - 9:57AM |
M24.00009: Brownian diffusion of wetted particle at fluctuating interface Xiao Xue, Mauro Sbragaglia, Luca Biferale, Federico Toschi We study the effects of thermally induced capillary waves on the diffusivity of a wetted particle at a fluctuating interface. Recent studies have shown that the wetted particle feels an unexpected viscous drag at the fluctuating interface which is larger than the one in the bulk. Our numerical investigations can address the problem by using a fluctuating multicomponent lattice Boltzmann (LB) model for non-ideal multicomponent fluids, including non-equilibrium stochastic fluxes mimicking the effects of molecular forces at the nanoscales coupled with wetted finite-size particle. We will present results on the Brownian diffusion for the wetted colloids both in bulk and at the fluctuating interface. Beyond the practical importance of our findings for kinetically driven assembly of particles, our study also explores a novel application of LB with colloid-fluid interactions in the realm of nanofluidic phenomena. |
(Author Not Attending)
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M24.00010: Emergent Structures in Colloidal Suspensions Sedimenting Down an Incline Aleksandar Donev, Blaise Delmotte, Joseph-Riley Cruise, Michio Tanaka, Michelle M Driscoll, Paul Chaikin The presence of a nearby no-slip boundary strongly affects the structures emerging in sedimenting colloidal suspensions. We combine experiments, theory and large scale numerical simulations to study the dynamics of colloidal suspensions sedimenting down an incline. By varying the inclination angle we observe different regimes of sedimentation. At low angles, when sedimentation is mostly directed toward the floor, the suspensions forms a monolayer with a dense traveling front. This traveling front can be described using a simple one dimensional nonlocal PDE. The front then transitions into finger-like structures whose width depends on the particle size and height from the floor. As the inclination angle increases, more and more particles are lifted away from the floor due to hydrodynamic interactions. The particle height distribution becomes bimodal: a second layer of more rapid particles forms, the fingers then move faster and exhibit a larger wavelength. After a characteristic time, the fingers sediment back on the incline, only to be lifted again by the flows generated by the particles at the rear. This cycle leads to unusual and rich long-time dynamics. |
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