Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session Y13: Friday: Frontiers in Soft MatterInvited
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Sponsoring Units: DSOFT Chair: Justin Burton, Emory University Room: Room 238 |
Friday, March 10, 2023 8:00AM - 8:36AM |
Y13.00001: Interplay of gross and fine morphologies of unstretchable balloons Invited Speaker: Mengfei He From high-altitude balloons to candy wrappers, planar sheets of thin films are commonly forced into doubly bent shapes. A key challenge is to understand the overall gross shape that is selected, and how it constrains the fine features, such as wrinkles, crumples, or creases. Here, we study a thin-membraned balloon as a prototypical system that involves a doubly curved gross shape with large amplitude undulations. By probing its profiles and cross sections, we discover that an existing geometric model developed for a film with small-scale wrinkles can capture the mean behavior of the film, even when the wrinkle amplitude is large. We then propose a minimal model for a representative balloon cross-section, as an elastic filament subjected to an effective pinning potential around the mean shape. Our parsimonious model reproduces a broad range of phenomena seen in the experiments, from morphological changes with pressure to the detailed shape of the wrinkles and folds. Our results establish a new route to analyzing finite buckled structures over an enclosed surface, which could aid the design of inflatable structures. |
Friday, March 10, 2023 8:36AM - 9:12AM |
Y13.00002: Coalescing Clusters Unveil New Regimes of Frictional Fluid Mechanics Invited Speaker: Haicen Yue Droplet coalescence is essential in a host of biological and industrial processes, involving complex systems as diverse as cellular aggregates, colloidal suspensions, and polymeric liquids. Classical solutions for the time evolution of coalescing clusters are typically based on tractable limiting physics, such as analytical solutions to the Stokes equation. By combining computational and theoretical analyses, we show that there is an unexplored family of coalescence processes: those governed by highly dissipative coupling to the environment. This leads to new scaling laws characterizing droplet coalescence, as well as new time-invariant parameterizations of the shape evolution of the coalescing system. We demonstrate these effects via particle-based simulations and both continuum and boundary-integral solutions to hydrodynamic equations, which we then understand in the context of a generalized Navier-Stokes-like equation. Our theoretical description of highly frictional coalescence mathematically maps onto Darcy flow in the presence of surface tension effects, opening up exciting avenues of research in applying well-studied fluid dynamical techniques to a broad range of novel systems. |
Friday, March 10, 2023 9:12AM - 9:48AM |
Y13.00003: Material constraints dictate flow mechanics in dense suspension rheology Invited Speaker: Shravan Pradeep Why are we able to walk on top of "Oobleck fluids" without sinking? What properties of a hillslope dictate its failure? Answer to these questions lie in the ability to link the macroscopic forcing to corresponding microstructural changes in a given soft material. The rearrangement dynamics of the constituent building blocks for a given complex fluid is controlled by the constraints between them. Using model hard-sphere suspensions and heterogenous real-life slurries, we study the effects of the particle surface roughness and the chemical composition in the dense suspension flow behavior. We find that a physics-informed universal parameter, jamming distance, can unify flow behaviors, both in linear and non-linear rheological regimes. Connecting structure-property relationships, leveraging steady-shear rheometry and confocal microscopy, we find that parameters that restrict the constraints in particle motion, such as frictional and cohesive interactions, modifies the jamming distance for a given suspension mixture and dictate the overall flow characteristics, for e.g., yielding or shear thickening. Our work provides a powerful framework to encode flow properties in dense suspensions comprising of colloidal and granular materials and has applications ranging from designing flow behavior in household products to better predicting geophysical flows. |
Friday, March 10, 2023 9:48AM - 10:24AM |
Y13.00004: Obstructed swelling and fracture of hydrogels Invited Speaker: Abigail Plummer Obstacles influence growth and expansion in a wide range of biological and non-biological processes, but isolating and understanding their impact can be difficult in complex systems. We study obstructed expansion in a simple system accessible with experiments, simulations, and theory---a crosslinked polymer network called a hydrogel swelling around fixed cylindrical pillars. In experiments, we observe that some obstacle geometries permit hydrogels to swell around the obstacles and remain intact, while other configurations force hydrogels to fracture as they expand. In order to predict which obstacle geometries are likely to prevent or promote fracture, we use finite element simulations to study the stresses that build up during swelling. Applying lessons from indentation theory, poroelasticity, and nonlinear continuum mechanics, we develop a theoretical framework for understanding how the maximum principal compressive and tensile stresses vary as a function of obstacle geometry in the long-time limit. |
Friday, March 10, 2023 10:24AM - 11:00AM |
Y13.00005: A bioinspired folding approach to assemble complex colloidal matter Invited Speaker: Angus McMullen When building blocks can move and stick to each other, they can self-assemble into new materials with exotic mechanical or optical properties. Researchers orchestrate colloidal self-assembly through careful design of an individual building block's geometry and interactions. The blocks assemble piece-by-piece, like a jigsaw puzzle that assembles itself. The problem with this approach is that the number of combinations is so vast that a unique structure requires that all particles be distinct. Instead, we fold a string of DNA-functionalized emulsion droplets into specific rigid geometries, analogous to how polypeptides fold into proteins. DNA-linked droplets are free to rearrange, allowing the system to reorganize and avoid kinetic traps. By imposing a hierarchy of interactions, we find that we can select structures with near-perfect yield even with basic interaction sequences. This non-equilibrium process allows for the selection of a desired state on the scale of minutes. This work presents an entirely new way to assemble colloidal structures and could be used to self-assemble mechanical or optical metamaterials. |
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