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 A09: Flow and Structure in Dense SuspensionsInvited Live
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Sponsoring Units: DSOFT Chair: Michelle Driscoll, Northwestern University; Xiang Cheng, University of Minnesota |
Monday, March 15, 2021 8:00AM - 8:36AM Live |
A09.00001: In sheared highly polydisperse emulsions, large droplets cause trouble for smaller droplets Invited Speaker: Eric Weeks We study experiments and simulations of highly polydisperse emulsions under shear flow. By highly polydisperse, we mean with the largest droplet diameters being as much as ten times the smallest diameters. We quantify non-affine motion in these highly polydisperse samples -- motion where droplets move with displacements distinctly different from their neighbors, or different from the overall imposed shear flow. The largest droplets typically move affinely, as if they are in a simple effective fluid formed by the other droplets. In contrast, the smallest droplets are often forced to move non-affinely by the larger droplets. We quantify how the non-affine motion diminishes as a function of droplet size and distance from the larger particles. We further show how the behavior depends on the overall droplet size distribution; in general, the largest droplets are always the troublemakers. Our main conclusion is that highly polydisperse samples behave qualitatively differently than weakly polydisperse samples. |
Monday, March 15, 2021 8:36AM - 9:12AM Live |
A09.00002: Fingering instabilities in confined suspensions Invited Speaker: Sungyon Lee We experimentally inject silicone oil into the mixture of oil and non-colloidal particles inside a Hele-Shaw cell, to investigate the connection between miscible fingering and the flow structure that develops inside the suspension. Previous studies with pure fluids have demonstrated that the onset of miscible fingering coincides with the transition from a smooth tongue-like structure to a sharp front between invading and defending fluids inside the thin gap. Our current experiments with suspensions reveal the same general behavior at the onset of miscible fingering in the continuum limit. However, beyond the onset, we observe the changes in morphologies of miscible fingering, as the channel confinement is systematically increased. Particularly, in the monolayer limit, we observe the emergence of fingering with two distinct wavelengths, which strongly depends on the local particle volume fraction. To qualitatively describe our experimental observations, we seek a kinetic theory that implements long-range hydrodynamic interactions. |
Monday, March 15, 2021 9:12AM - 9:48AM Live |
A09.00003: Force networks in shear thickening suspensions Invited Speaker: Jeffrey Morris The strong shear thickening exhibited by near-hard sphere suspensions has features of a phase transition, with strong fluctuations of the stress at fixed shear rate in the vicinity (with respect to both solid fraction and shear rate) of the onset of shear thickening. In our studies based on simulations which capture the viscous-to-frictional rheology transition, a notable feature is that the high- and low-stress states do not show significant differences in typical measures of their spatial correlation: e.g., the pair distribution function differs only slightly between the two. However, the contact force networks that develop as the result of shear stress driving particles into contact against an opposing repulsive interparticle force show distinct changes across this transition, and their statistics give insight to the features that allow a single volume fraction to offer remarkably different resistance to flow, from smoothly flowing at small stress to very viscous or even fully jammed at high stress. Results from persistent homology tools, k-core analysis, and tools of statistical mechanics will be presented to elucidate some new features of dense suspension shear thickening. |
Monday, March 15, 2021 9:48AM - 10:24AM Live |
A09.00004: Conching chocolate as a protoypical example of poweder incorporation Invited Speaker: Wilson Poon The mixing of a powder of 10- to 50-μm primary particles into a liquid to form a dispersion with the highest possible solid content is a common industrial operation. Building on recent advances in the rheology of such “granular dispersions,” we study a paradigmatic example of such powder incorporation: the conching of chocolate, in which a homogeneous, flowing suspen- sion is prepared from an inhomogeneous mixture of particulates, triglyceride oil, and dispersants. Studying the rheology of a simplified formulation, we find that the input of mechanical energy and staged addition of surfactants combine to effect a consid- erable shift in the jamming volume fraction of the system, thus increasing the maximum flowable solid content. We discuss the possible microscopic origins of this shift, and suggest that choco- late conching exemplifies a ubiquitous class of powder–liquid mixing. |
Monday, March 15, 2021 10:24AM - 11:00AM Live |
A09.00005: Suspensions of non-Brownian particles in complex fluids: Rheology, microstructure and fluid mechanics Invited Speaker: Sarah Hormozi Suspensions of non-Brownian particles in complex fluids (hereafter complex slurries) are relevant in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). It is also relevant to mention that some biological and smart materials can be designed from various suspensions, drawing attention to applications in physiology, bio-locomotion and shock absorbers. This countless number of suspensions has a wide range of nonlinear rheological behaviors, such as shear thinning, shear thickening, shear banding, yield stress, and finite normal stress differences even when inertia is negligible. |
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