Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session Y24: Suspensions DynamicsLive
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Sponsoring Units: DFD Chair: Larry Galloway, University of Pennsylvania |
Friday, March 19, 2021 11:30AM - 11:42AM Live |
Y24.00001: Three-Step Relaxation in Stabilized Dense Suspensions Andrew Griese, Jae Hyung Cho, Ivo R Peters, Irmgard Bischofberger Stabilized dense suspensions of solid particles in Newtonian fluids exhibit a variety of non-Newtonian behaviors depending on the shear stress applied to the suspension and the particle mass fraction. Suspensions at sufficiently high particle concentration shear-thicken dramatically and can even exhibit solid-like behavior. How dense suspensions relax out of such stressed rheological states, however, is not well understood. Using a texture analyzer, we vary the parameters of the stressed states and measure the suspension’s relaxation response. We find three distinct relaxation regimes; a rapid high stress decay followed by two exponential decay regimes. Combining our findings with rheological data allows us to establish the mechanisms governing each regime. |
Friday, March 19, 2021 11:42AM - 11:54AM Live |
Y24.00002: Fluid rheological effects on dielectrophoretic focusing and trapping of particles in a constricted microchannel Joseph Bentor, Amirreza Malekanfard, Xiangchun Xuan Microfluidic devices have been extensively used for particle focusing and trapping in chemical and biomedical applications in recent years. Insulator-based dielectrophoresis (iDEP) is an emerging technique that controls particles via dielectrophoresis induced by the strong electric field gradients around insulating structures. However, studies on particle manipulation in iDEP microdevices have been limited to Newtonian fluids. This work reports an experimental study of the individual and combined effects of fluid elasticity and shear thinning on particle manipulation through a constricted microchannel. Five types of non-Newtonian fluids with distinct rheological properties are tested, including xanthan gum (XG), polyvinylpyrrolidone (PVP), polyethylene oxide (PEO), hyaluronic acid (HA) and polyacrylamide (PAA) solutions. The dielectrophoretic force is of purely electric origin, and hence should be independent of the fluid rheology. However, the observed particle focusing and trapping phenomena are significant different among the prepared non-Newtonian fluids though they are all dilute polymer solutions in the same electrolyte buffer. |
Friday, March 19, 2021 11:54AM - 12:06PM Live |
Y24.00003: Effects of Brownian diffusion on dynamics of concentrated suspensions of ideally conductive particles in an electric field Siamak Mirfendereski, Jae Sung Park Employing a concentrated suspension of small conductive particles such as a carbon slurry has gained a growing interest in various energy storage and desalination applications, including flowable battery electrodes, and flow-based capacitive deionization. The performance of these systems depends highly on particle concentration and size in the slurry. To this end, we use a large-scale numerical simulation to study the dynamics of ideally conductive Brownian particles in a suspension placed in a uniform electric field. In this system, the particles undergo a non-linear electrokinetic phenomenon termed as dipolophoresis (DIP), which is the combination of dielectrophoresis and induced-charge electrophoresis, as well as Brownian diffusion. Here, the effects of particle size and concentration are presented. The particle size is expressed as Péclet number (Pe), a ratio of the particle motion due to the electrokinetics and Brownian diffusion. Our previous study shows the non-trivial behaviors at concentrated DIP suspensions, such as an increase in suspension diffusivity. It appears that the Brownian effect diminishes these behaviors, and its predominance occurs at Pe < 5, which will be further discussed. |
Friday, March 19, 2021 12:06PM - 12:18PM Live |
Y24.00004: Measuring the Dynamic Material Properties of Drying Paint through Microrheology Maria Chiara Roffin, Christopher Wirth, Steven Barancyk, Reza Rock, James F Gilchrist Studying rheological properties during drying of paint is important for controlling defect formation in the coating as well as connecting alterations in formulation to final paint performance. Passive microrheology, the tracking of the Brownian motion of tracers to determine the fluid material properties, is used to study both quiescent and drying thin films of a model paint where conditions such as molecular weight and composition are modified. Drying paint can experience convection due to Marangoni stresses, where the random fluctuations of tracers are superimposed on the kinematic motion of the fluid. This convective flow can be detrimental to the analysis of tracers’ mean squared displacement (MSD). Different methods are used to eliminate these effects, such as de-drifting algorithms, where the mean displacements were subtracted from a particle’s trajectory, or calculating the relative mean squared displacement (rMSD), where fluctuations of particles’ position are tracked in separation distance rather than absolute MSD. MSD, rMSD, and de-drifting are compared across various convection profiles to determine the appropriate approach to characterize the evolving material properties during drying. |
Friday, March 19, 2021 12:18PM - 12:30PM Live |
Y24.00005: Time dependence of advection-diffusion coupling for nanoparticle ensembles Alexandre Vilquin, Vincent Bertin, Pierre Soulard, Gabriel Guyard, Elie Raphael, Frederic Restagno, Thomas Salez, Joshua D. McGraw Advection-diffusion coupling can enhance particle dispersion by orders of magnitude as compared to pure diffusion, with a steady state being reached for confined flow regions such as a blood vessel. Whereas the classical Taylor model predicts the long-time limit of this dispersion in a closed space, we address the question of the dynamics in the first instants after release and the corresponding crossover towards the long-time limit. Here by using evanescent wave microscopy, we make time-dependent, nanometrically-resolved particle dispersion measurements varying particle size, velocity gradient, and viscosity in a submicrometric flow domain. We measure the full dynamical approach and crossover into the steady state, revealing a family of universal curves, depending on the initial spatial distribution of the particles. Such laws are essential in predicting and optimizing the efficiency of drug delivery, among others. |
Friday, March 19, 2021 12:30PM - 12:42PM Live |
Y24.00006: Pattern formation in localized photo-bioconvection Aina Ramamonjy, Julien Dervaux, Philippe Brunet Many photosynthetic micro-organisms are able to detect light and move towards optimal light intensities, an ability known as phototaxis. In suspensions of phototatic micro-algae Chlamydomonas Reinhardtii, it was demonstrated that using a thin localized light beam to attract and accumulate cells could induce macroscopic recirculation flows referred to as localized photo-bioconvection flows. Here, we study the associated concentration patterns. The cells being slightly denser than their surrounding fluid, bioconvection originates from spatial gradients of cell concentration which create density inhomogeneities. A dimensionless Rayleigh number compares buoyancy-driven convection over diffusion. While spontaneous (without light excitation) bioconvection occurs in suspensions of on average upward swimming micro-organisms only above a critical Rayleigh number, it was shown that localized photo-bioconvection occurs below this threshold. In the present study, we show that when the beam width is wider than the suspension depth, the concentration field exhibits remarkable symmetry breakings. |
Friday, March 19, 2021 12:42PM - 12:54PM Live |
Y24.00007: Multi-scale dynamics of colloidal deposition and erosion in porous media Navid Bizmark, Joanna Schneider, Rodney Priestley, Sujit Datta Diverse processes—e.g., environmental pollution, groundwater remediation, oil recovery, filtration, and drug delivery—involve the transport of colloidal particles in porous media. Using confocal microscopy, we directly visualize this process in situ and thereby identify the fundamental mechanisms by which particles are distributed throughout a medium. At high injection pressures, hydrodynamic stresses cause particles to be continually deposited on and eroded from the solid matrix—strikingly, forcing them to be distributed throughout the entire medium. By contrast, at low injection pressures, the relative influence of erosion is suppressed, causing particles to localize near the inlet of the medium. Unexpectedly, these macroscopic distribution behaviors depend on imposed pressure in similar ways for particles of different charges, even though the pore-scale distribution of deposition is sensitive to particle charge. These results reveal how the multi-scale interactions between fluid, particles, and the solid matrix control how colloids are distributed in a porous medium. |
Friday, March 19, 2021 12:54PM - 1:06PM Live |
Y24.00008: Squeezing multiple soft particles into a constriction: transition to clogging Clément Bielinski, Othmane Aouane, Jens Harting, Badr Kaoui Flows of particles are largely encountered in microfluidic devices designed to manipulate micro-sized artificial particles or living cells. As the particle size is generally the same order as the channel width, the performance of such devices could dramatically be hindered by clogging events. While there is an increasing need to improve the capability of microfluidic devices to handle high throughput, this study is carried out to address the scenarios that emerge when multiple soft particles flow through a microfluidic constriction. |
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