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 M07: Microflows Meet Soft Matter: Compliance, Growth, Instabilities and BeyondFocus Live
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Sponsoring Units: DSOFT DFD GSNP Chair: Pejman Sanaei, New York Inst of Tech Room: 07 |
Wednesday, March 17, 2021 11:30AM - 12:06PM Live |
M07.00001: Viscous flows with thin, compliant boundaries Invited Speaker: Dominic Vella Viscous fluids flowing in channels with solid, but compliant, boundaries are common in a range of biological and industrial settings. The presence of flexibility can qualitatively alter the behaviour of such systems, forcing us to revisit basic principles with which such viscous flows are usually understood: the reversibility of Stokes flow no longer holds and the relationship between flux and driving pressure may be nonlinear. In other situations, the mere presence of boundary compliance, combined with capillarity is enough to spontaneously generate fluid motion. I will give examples of some of these unusual behaviours, focussing on situations in which the compliant boundary is in some sense thin, as well as discussing the validity of the different models of boundary deformation. |
Wednesday, March 17, 2021 12:06PM - 12:18PM Live |
M07.00002: On mathemathical modeling of flow and fouling in elastic membrane filters Pejman Sanaei, Shi Yue Liu, Zhengyi Chen, Ivan Christov In this work, we present a mathematical model of an elastic membrane filter with multi-layer bifurcating interior morphology. Two pervasive filtration forcing mechanisms are considered: (i) constant pressure drop; and (ii) constant flux through the membrane. We investigate how filtration behave under these two forcing mechanisms and describe the morphology change due to fouling coupled to membrane pore elasticity. Simulations are conducted under the constant flux condition and then switched to the constant pressure scenario after the pressure reaches a certain threshold. We also compare the results to membranes with no elasticity and analyze the filtration efficiency under different membrane materials. |
Wednesday, March 17, 2021 12:18PM - 12:30PM Live |
M07.00003: Interaction and coalescence of fluid-driven fractures: numerical predictions versus experiments Carlo Peruzzo, Brice Lecampion, Niall O'Keeffe, Paul F Linden The coalescence of two coplanar fractures growing under the symmetric injection of a Newtonian fluid from two point sources provides a unique data set to validate theoretical predictions of hydraulic fracture (HF) growth. |
Wednesday, March 17, 2021 12:30PM - 12:42PM Live |
M07.00004: State and Rate Dependent Contact Line Dynamics over an Aging Soft Surface Dongshi Guan, Elisabeth Charlaix, Penger Tong We report direct atomic-force-microscope measurements of capillary force hysteresis (CFH) of a circular contact line (CL) formed on a micron-sized glass fiber, which is coated with a thin layer of soft polymer film and intersects a water-air interface. The measured CFH shows a distinct overshoot for the depinning of a static CL, and the overshoot amplitude grows logarithmically with both the hold time and fiber speed. A unified model based on the slow growth of a wetting ridge and force-assisted barrier crossing is developed to explain the observed time (or state) and speed (or rate) dependent CL depinning dynamics over an aging soft surface. The experimental findings have important implications for a common class of problems involving depinning dynamics in a defect or roughness landscape, such as friction of solid interfaces. |
Wednesday, March 17, 2021 12:42PM - 12:54PM Live |
M07.00005: Capillary control of failure in soft composite materials Marc Suñé, John Scott Wettlaufer A solid subjected to an in-plane compression buckles when the compressing load reaches a critical value and an infinitesimal deformation leads to a large amplitude out-of-plane deflection. Since Euler’s original study on the elastic instability of a column subjected to longitudinal compressing forces at its ends, buckling has been extensively studied in homogeneous, isotropic, linear-elastic solids. Here, we examine the nature of the buckling in inhomogeneous soft composite materials. In particular, we consider a soft host with liquid inclusions both large and small relative to the elastocapillarity length, which lead to softening and stiffening of a homogeneous composite respectively. By imposing a gradient of the liquid volume fraction or varying the inclusion size we tailor the elastic behavior spatially, and hence we can deliberately manipulate the failure properties of the elastic composite. We have applied this setup to the study of the buckling of compressed columns as well as thin sheets floating on a liquid. |
Wednesday, March 17, 2021 12:54PM - 1:06PM Live |
M07.00006: Gel rupture in a dynamic environment Kelsey-Ann Leslie, Robert Doane-Solomon, Srishti Arora, Sabrina Curley, Caroline Rose Szczepanski, Michelle R Driscoll Polymer hydrogels have been and continue to be used in a wide range of applications in different fields. Due to the structure of these materials, the absorption of water will usually result in uniform swelling, which scales with the degree of cross-linking. These features make hydrogels prime candidates for biosensors, drug delivery vectors, and carriers for cells in tissue engineering. Most past studies into the mechanics of hydrogels typically observed the materials in two separate states: (1) unswollen and without any solvent, or (2) in an equilibrium swelling state where the maximum amount of water has been imbibed. In this experimental study, we observe the dynamic process of swelling and how internal stresses that develop during swelling lead to the subsequent rupture of the poly(ethylene glycol)-based hydrogels. We find that rupture events follow a three-stage process that includes a waiting period, a slow fracture period, and a final stage in which a rapid increase in the velocity of crack propagation is observed. We describe this fracture behavior based on changes in material properties that occur during swelling, and highlight how this rupture behavior can be controlled by straight-forward modifications to the hydrogel network structure. |
Wednesday, March 17, 2021 1:06PM - 1:18PM Live |
M07.00007: Tunable viscoelasticity of double gel networks: colloidal gel embedded in a hydrogel matrix Ippolyti Dellatolas, Jae Hyung Cho, Irmgard Bischofberger
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Wednesday, March 17, 2021 1:18PM - 1:30PM Live |
M07.00008: Spontaneous formation of chiral domains in a flowing achiral nematic liquid crystal Qing Zhang, Rui Zhang, Irmgard Bischofberger An achiral nematic fluid in a confined geometry could be expected to form achiral structures in a pressure driven flow. Surprisingly, we find the spontaneous emergence of chiral structures when an achiral lyotropic chromonic liquid crystal (LCLC) in the nematic phase relaxes from a high velocity flow to a steady state lower velocity flow. The chirality results from a periodic twist deformation of the liquid crystal and leads to striking stripe patterns vertical to the flow direction. We demonstrate that this occurrence of chiral structures can be rationalized by the disparate elastic constants of the LCLC; the peculiarly low twist elastic constant and saddle splay elastic constant compared to the bend elastic constant of LCLCs allow for twist deformations. We show that the pitch length of the chiral domains depends on the local flow velocity. |
Wednesday, March 17, 2021 1:30PM - 1:42PM Live |
M07.00009: Label-free microfluidic platform for adhesion-based cell sorting Fatima Ezahra Chrit, Todd Sulchek, Alexander Alexeev Identifying and isolating cells that express desired molecular surface markers is required in a variety of applications in the biological sciences, cell therapy, and medical diagnostics. We develop a microfluidic approach for high-throughput and label-free sorting of cells by their affinity for target ligands by molecular surface markers. We use computational modeling to examine cells adhesion kinetics at ultrafast timescales in the microfluidic channel that is decorated with periodic skewed ridges coated with adhesive molecules. Binding events can induce differential cell trajectories resulting in cell separation based on molecular affinity and molecular surface density. The approach can enable direct measurements of transient interactions between important physiological ligands and adhesive cell molecules that will benefit the development of novel diagnostic methods. |
Wednesday, March 17, 2021 1:42PM - 1:54PM Live |
M07.00010: Method for Characterizing Microscopic Void Structure in Porous Media Brian Ryu, Roseanna Zia Transport of molecules and particles in porous media is ubiquitous in industrial and biophysical systems, where specific pore morphologies are utilized for selective filtering. Mass transport through porous media is commonly modeled at the macroscopic scale by abstracting the interior morphology of the medium into effective quantities that describe flow hindrance. While these methods are successful in predicting macroscopic properties such as permeability, they are not as well suited for modeling and predicting heterogenous transport, where the tortuous structural features of the material must be represented in detail. We have developed a method for obtaining a detailed quantitative structural description of void structures in a porous medium. Our method includes the construction and analysis of Voronoi diagrams, from which we determine a network of all possible void paths and their widths throughout the system. These networks can be further analyzed to determine the size-dependent migration rate of liquid-borne particles migrating through the material. We validate our results using Brownian dynamics simulations of tracer colloids of various sizes diffusing in the voids of a colloidal gel that show excellent agreement between predicted cutoff sizes and diffusive behavior. |
Wednesday, March 17, 2021 1:54PM - 2:06PM On Demand |
M07.00011: Compliance-effects in viscous streaming Yashraj Bhosale, Tejaswin Parthasarathy, Mattia Gazzola Rectified flows associated with the oscillatory motion of immersed solid boundaries, known as viscous streaming, are an efficient way of manipulating and controlling fluids via inertial effects in microfluidic settings. Despite its potential, we know surprisingly little about viscous streaming beyond the classical cases of vibrating solid cylinders, plates, and spheres. Here we extend our understanding by numerically investigating the effects of solid-boundary elasticity, via a recently developed framework based on remeshed vortex methods coupled to an inverse map technique. Preliminary results indicate that a complex interplay between inertial, viscous, and elastic forces leads to rich behaviors, which can potentially be exploited to expand our control of the streaming field than was previously possible. |
Wednesday, March 17, 2021 2:06PM - 2:18PM On Demand |
M07.00012: Formation, growth and coalescence of nanoscopic mesas in stratifying foam films Chenxian Xu, Vivek Sharma Ultrathin micellar foam films exhibit stratification due to confinement-induced structuring and layering of micelles. Stratification proceeds by the formation and growth of thinner domains at the expense of surrounding thicker film, and flows and instabilities drive the formation of nanoscopic terraces, ridges and mesas within a film. The detailed mechanisms underlying stratification are still under debate, and are resolved in this contribution by addressing long-standing experimental and theoretical challenges. Thickness variations in stratifying films are visualized and analyzed using interferometry, digital imaging and optical microscopy (IDIOM) protocols, with unprecedented high spatial (thickness \textless 100 nm, lateral \textasciitilde 500 nm) and temporal resolution (\textless 1 ms). Using IDIOM protocols we developed recently, we characterize the shape and the growth dynamics of mesas that flank the expanding domains in micellar thin films, and we track their evolution, as well as coalescence dynamics. |
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