Bulletin of the American Physical Society
APS March Meeting 2018
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session A46: Flow of Complex Fluids, Polymers, Gels and Granular Material |
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Sponsoring Units: DFD GSNP Chair: Hadi Mohammadigoushki, Florida State University Room: LACC 506 |
Monday, March 5, 2018 8:00AM - 8:12AM |
A46.00001: Transient Shear Banding of Wormlike Micellar Solutions Alireza Dalili, Hadi Mohammadigoushki We report experiments on a simple shear flow of a model shear banding wormlike micellar solution with a custom-built Taylor-Couette (TC) cell. The wormlike micellar solution contains cetyl trimethyl ammonium bromide (CTAB) and sodium salycilate (NaSal). Rheological measurements indicate formation of a shear stress plateau for 0.004 <shear rate< 1 (1/s) at 22 °C. Transient evolution of the velocity profile is investigated from rest using a step shear. Shear stress experiences an overshoot followed by an undershoot and finally steady state. Negative velocity is observed during the undershoot. The steady state velocity profile in θ-r plane of the TC cell confirmed formation of a shear banded velocity profile with no wall-slip at the moving boundary and the proportion of the high shear band compared well with the lever rule. |
Monday, March 5, 2018 8:12AM - 8:24AM |
A46.00002: Buckling and migration of semi-flexible filaments Brato Chakrabarti, David Saintillan, Yanan LIU, Anke Lindner, Olivia du Roure The dynamics of polymeric fluids exhibit rich and sometimes counter-intuitive behaviors, which can be traced back to the complex conformations of polymer molecules in shear flow. The tumbling of rigid bodies in shear flow at low Reynolds number has been understood since the pioneering work of Jeffery. The effect of polymer chain flexibility, however, has non-trivial consequences in this classical problem. Here we study the dynamics of actin filaments, which are semi-flexible filaments usually found in the cell cytoplasm, in an externally applied simple shear flow. We model these inextensible filaments using Euler-Bernoulli beam and use nonlocal slender body theory (SBT) in the presence of Brownian fluctuations to probe their dynamics, and compare our numerical simulations to microfluidic experiments. We systematically explore the parameter space by varying the length of the polymer and changing the shear rate. A series of conformational transitions is observed with increasing shear rate, from quasi-periodic tumbling to nontrivial buckling regimes due to the destabilizing effect of compressive viscous forces, and physical mechanisms are proposed for these transitions. |
Monday, March 5, 2018 8:24AM - 8:36AM |
A46.00003: Pearling Instabilities of a Visco-Elastic Thread Antoine Deblais, Krassimir Velikov, Daniel Bonn Pearling instabilities of slender visco-elastic threads has received much attention, but remain incompletely understood. We study the instabilities in polymer solutions subject to uniaxial elongational flow. Two distinctly different instabilites are observed: beads-on-a-string and blistering. The beads-on-a-string structure arises from a capillary instability whereas the blistering instability has a different origin: it is due to a coupling between stress and polymer concentration. By varying the temperature to change the solution properties we elucidate the interplay between flow and phase separation. |
Monday, March 5, 2018 8:36AM - 8:48AM |
A46.00004: Filament Dynamics in Salt-free Viscoelastic Surfactant Solutions Rose Omidvar, Hadi Mohammadigoushki In this work, we study the dynamics of a model wormlike micellar solutions via CaBER, shear rheology and TEM imaging. Wormlike micellar solutions contain cetyltrimethylammonium tosylate (CTAT) in deionized water. At low concentrations (0.7 wt% < c < 1.1 wt%,), solutions exhibit shear thickening and elongational flow shows formation of elastic filaments possibly due to formation of elongation induced structures. In this range of concentrations, the extensional relaxation time is fairly constant around 0.03 s. At higher concentrations 1.1 wt% < c < 2-3 wt%, a significant increase in shear relaxation time is observed. However, beyond 2 wt%, the shear relaxation time decreases and the zero shear viscosity approaches an asymptotic value. TEM images confirm no sign of branched networks beyond the concentration of 2 wt%. It is shown that the maximum Trouton ratio measured from transient rheology experiments decreases as concentration increases and finally reaches a constant value around Tr ≈ 3 for c > 2 wt%. |
Monday, March 5, 2018 8:48AM - 9:00AM |
A46.00005: Experimental investigation of jamming in porous media by microgel suspensions. Swati Kaushik, Guillaume Ovarlez, Steven Meeker, Hugues Bodiguel Suspension flows in porous media are used in many industrial applications. Clogging of the porous media and suspension's filtration are key issues encountered in these applications. These phenomena are complex processes and in order to get a better understanding of them, we perform experiments to investigate the jamming dynamics of microgel suspensions in microfluidic devices to mimic model porous media. We study how parameters like surface wettability, particle concentration, particle size and flow rates affect the filter cake formation. We exploit phase contrast microscopy for direct observation of the clogging of porous media by microgel particles. In situ Raman spectroscopy is also used to determine the local concentration of the jammed microgel in the filter cake inside the microfluidic geometry. Additionally, we investigate the rheological behavior in microchannels to understand the effect of confinement on the rheology. Our experiments reveal that the microgel particles have more affinity for a hydrophilic surface which eventually assists in jamming. We report that the rate of formation of the filter cake for cross flow filtration geometry is dependent on pore size/ particle size ratio. |
Monday, March 5, 2018 9:00AM - 9:12AM |
A46.00006: Diffusiophoresis in confined geometries Jesse Ault, Sangwoo Shin, Howard Stone Flows containing dissolved solutes and suspended particles are found in porous media systems including aquifers, hydraulic fractures, filtration systems, and others. Solute concentration gradients can induce surprising dynamics to charged suspended particles through the action of diffusiophoresis. Through this effect, particle motions can be directed towards hard-to-reach geometries, and particles can achieve high concentrations and even clog systems. We present a diffusiophoretic approach to dramatically enhance the penetration of charged particles into confined geometries. Furthermore, we demonstrate a low-cost zeta potentiometry technique that allows the simultaneous measurement of particle and wall zeta potentials. We develop solutions for the particle dynamics in pores, and use the method of characteristics to predict particle trajectories. Results confirm the build up of maxima and minima in the propagating particle dynamics. We demonstrate systems that can rapidly concentrate particles. Results inform the design of applications to enhance particle motions in pores, and the techniques presented can be used to preconcentrate biomolecules for rapid bioassays. |
Monday, March 5, 2018 9:12AM - 9:24AM |
A46.00007: Stress modeling in suspensions undergoing hetergeneous flows Benjamin Dolata, Roseanna Zia We present a theoretical study of the stress tensor for a colloidal dispersion undergoing non-viscometric flow. In such flows, the non-homogeneous suspension stress depends on not only the local average total stresslet—the sum of symmetric first moments of both the hydrodynamic traction and the interparticle force—but also on the average quadrupole, octupole, and higher-order moments. To compute the average moments, we formulate a six dimensional Smoluchowski equation governing the microstructural evolution of a suspension in an arbitrary fluid velocity field. Under the conditions of rheologically slow flow, where the Brownian relaxation of the particles is much faster than the spatiotemporal evolution of the flow, the Smoluchowski equation permits asymptotic solution, revealing a suspension stress that follows a second-order fluid constitutive model. We obtain a reciprocal theorem and utilize it to show that all constitutive parameters of the second-order fluid model may be obtained from two simpler linear-response problems: a suspension undergoing simple shear and a suspension undergoing isotropic expansion. The consequences of relaxing the assumption of rheologically slow flow, including the appearance of memory and microcontinuum behaviors, are discussed. |
Monday, March 5, 2018 9:24AM - 9:36AM |
A46.00008: Shock Instability and Pattern Formation in Vertically Oscillated Granular Media Jonathan Bougie A layer of grains atop a plate subject to vertical shaking will leave the plate at some time during the oscillation cycle provided that the accelerational amplitude of the plate’s oscillation is greater than the acceleration of gravity. With each subsequent contact of the grains with the plate, shocks form and propagate through the granular layer. Additionally, when the dimensionless accelerational amplitude Γ exceeds a critical value Γ_{crit}, standing-wave patterns form in the layer, oscillating subharmonically with respect to the oscillation of the plate. We explore the relationship between these shocks and patterns by modeling granular flow using numerical simulations of continuum equations to Navier-Stokes order. These simulations provide a basis to characterize the shocks in these layers and to analyze pattern development in connection with an instability in the shock front as it propagates through the layer. |
Monday, March 5, 2018 9:36AM - 9:48AM |
A46.00009: Can we reconcile Steady State Rheology with Impact Dynamics for Shear Thickening Suspensions? Niveditha Samudrala, Eric Brown Discontinuous Shear Thickening (DST) suspensions behave as typical liquids at low shear rates but exhibit solid-like features, e.g. resistance to flow and cracking, beyond a critical shear rate in steady-state rheology. A standard assumption is that stress measured in rheometer measurements can be used to predict flows in other geometries. The maximum stresses supported by a sample beyond the critical shear rate is O (10^3) Pa in a rheometer. In contrast, DST suspensions can support larger stresses of O (10^6) Pa under impact. Recent impact studies reveal a dynamically jammed region below the impactor. We find that the front velocity of this region is nearly the same as the impact velocity up until a critical impact velocity. Beyond this critical velocity, we find that the front velocity increases with the impact velocity before hitting a plateau. We further investigate the relationship between the critical velocity from impact experiments and the critical shear rate from rheology measurements in an effort to understand the mismatch in the stress scales. |
Monday, March 5, 2018 9:48AM - 10:00AM |
A46.00010: Collapse of Granular Column: Influence of Particle Shape and Polydispersity Denis Dumont, Paul Rambach, Pascal Damman In spite of a large effort of the scientific community, a global description of the rheology of granular assembly remains largely elusive. For instance, a systematic study of the influence of particle shape and polydispersity is still lacking while their drastic influence has been demonstrated. To gain a better insight into the mechanical behavior of granular matter, we focus on a canonical set-up: the collapse of columns under gravity. We carried on 3D DEM numerical simulations and experiments of collapses for various granular columns on a frictional plane. Our observations accurately reproduce the previously reported data, the height and run-out distance are determined by the aspect ratio, a=H_{i}/R_{i}, of the column. It appears however that the final morphology of the pile is dictated by the existence of a small region of static grains at the bottom of the column. The collapse occurs by a dense flow of falling grains onto the cone of static grains. In this presentation, we will discuss the origin of this static zone and how it influences all the properties of the granular pile during the collapse. A peculiar attention will be drawn to the particle shape. |
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