Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session S11: Flow of Complex Fluids, Rheology Structures and Instabilities IRecordings Available

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Sponsoring Units: DFD Chair: Linda Hurst, University of California Merced Room: McCormick Place W181B 
Thursday, March 17, 2022 8:00AM  8:12AM 
S11.00001: Sedimentation in a chiral fluid with odd viscosity Tali Khain, Colin R Scheibner, Michel Fruchart, Vincenzo Vitelli Chiral particles do not sediment in the same way as spherical ones. We ask, what if the fluid is chiral instead of the particle? In particular, we explore the modifications to Stokes flow due to coefficients of the viscosity tensor which are parityviolating (not invariant under mirror reflections of space) and nondissipative (i.e. odd). We find that, in the Stokeslet flow, as well as in other cylindrically symmetric systems, the velocity field acquires an azimuthal component due to the additional viscosity coefficients. When treating each sedimenting particle as a Stokeslet, we show that the hydrodynamic interaction between two particles is changed as the azimuthal flow bends the particle trajectories in a manner not present in a standard fluid. For a spherical cloud of thousands of particles, the azimuthal flow impedes the transformation into a torus and the subsequent breakup that would otherwise occur. The basic mechanisms explored here are relevant for sedimentation in fluids under rotation, a magnetic field, and in fluids with internal activity, in which parityviolating viscosities have been experimentally demonstrated. 
Thursday, March 17, 2022 8:12AM  8:24AM Withdrawn 
S11.00002: Viscous fingering in polymeric fluids Paresh Chokshi, Pooja Jangir, Ratan Mohan The flow displacement process, through microchannel or porous media, suffers from a fingering phenomenon that manifests in the form of fingerlike patterns around the interface region. Viscous fingering instability can be controlled by adding polymers to either displacing or displaced fluid which alters the fluid viscosity, the cause for viscous fingering. The shearrate dependent viscosity and elasticity of polymeric fluids influence the growth of fingers mainly due to nonuniform viscosity distribution. To investigate the role of rheological properties on instability, the miscible flow displacement is studied experimentally using the HeleShaw cell. The aqueous solutions of polyethylene oxide (PEO) of varying concentrations and molecular weights are used as one of the fluids. The visualization of fingers shows that displacement of PEO solutions at high concentration or high molecular weight leads to more complex and fractallike patterns with tipsplitting and sidebranching mechanisms. For similar viscosity contrast between two fluids, the finger formation is found to be more intensified when displaced fluid is polymeric in nature as compared to displacing fluid being polymeric fluid. The shearthinning behavior strengthens shielding behavior whereas fluid elasticity leads to tipspitting, irrespective of the flow arrangement. 
Thursday, March 17, 2022 8:24AM  8:36AM 
S11.00003: Effect of rotational shear on the viscous fingering instability in miscible fluids Samar Alqatari, Zhaoning Liu, Thomas E Videbaek, Sidney R Nagel When a fluid is injected into a more viscous one in the thin gap between the two plates of a HeleShaw cell, the interface between the fluids can become unstable to the growth of long protrusions. We use miscible fluids in a radial HeleShaw geometry to study the instability in the presence of an oscillatory rotational shear between the plates. The rotational shear delays the onset of the instability and creates broader fingers. We study how these effects depend on the amplitude and frequency of the shear, and on the injection rate and viscosity ratio of the two fluids. We use simulations to investigate how the shear alters the interface in the direction of the thin gap between the plates. 
Thursday, March 17, 2022 8:36AM  8:48AM 
S11.00004: Growth of fluiddriven fractures in the viscousdominated regime Sri Savya Tanikella, Emilie Dressaire We revisit the classical problem of a growing pennyshaped fracture formed upon injection of viscous fluid in a brittle solid. We report an experimental study on the injection of a viscous fluid at a constant flow rate. The fracture’s growth dynamics is controlled by the viscous dissipation in the fluid. Previous studies have shown discrepancies between theoretical predictions and experimental results. Our experiments show that the radius increases even after the injection is stopped, until it reaches an equilibrium value. We measure the fracture width and radius over time, for varying mechanical properties of the gel and injection parameters. The viscosity of the injected fluid, the injection flow rate and the total volume injected influence the fracture dynamics. Scaling arguments are provided to explain the experimental results and provide insights into the underlying physics. 
Thursday, March 17, 2022 8:48AM  9:00AM 
S11.00005: Electricallycontrolled selfsimilar evolution of viscous fingering patterns in radial HeleShaw flows Pedro Anjos Timedependent injection strategies are commonly employed to control the number of viscous fingers emerging at the interface separating two fluids during radial displacement in HeleShaw flows. Here we demonstrate theoretically that such a usual controlling method is significantly improved by taking advantage of an electroosmotic flow generated by applying an external electric field. More specifically, under the coupled action of timevarying electric currents and injection rates, we design a strategy capable of controlling not only the number of fingers emerging at the interface but also when (and if) the selfsimilar evolution occurs. In addition, the level of instability of the nfold fingered patterns can also be tuned. This improved control over the interfacial features cannot be realized by the sole consideration of a timevarying injection rate. Perturbative secondorder modecoupling analysis and boundary integral simulations confirm that the validity and effectiveness of the controlling protocol go beyond the linear regime. 
Thursday, March 17, 2022 9:00AM  9:12AM 
S11.00006: Viscous fingering stabilization in miscible fluids under oscillatory translational shear Zhaoning Liu, Samar Alqatari, Thomas E Videbaek, Sidney R Nagel Viscous fingering occurs when one fluid penetrates a second one of higher viscosity in the narrow gap between the two plates of a HeleShaw cell. Using miscible fluids in a radial geometry, we study the onset and growth rate of fingers while an oscillatory, translational shear is applied between the two plates. This shear changes the interfacial structure between the fluids in the thin dimension traversing the gap and thus decreases the viscosity contrast at the interface. In the direction parallel to the shear axis, the finger length is suppressed and the instability onset is delayed as the shear rate and amplitude are increased. We extract the relevant length and time scales leading to stabilization by varying the gap size and fluidinjection rate over a wide range of fluid viscosity ratios. We present results from experimentally validated simulations to show the structure in the gap. 
Thursday, March 17, 2022 9:12AM  9:24AM 
S11.00007: The Role of Interlayer Spacing in Fluid Permeability of Barrier Materials with 2D Inclusions Chunzhi Wu, Gerald J Wang A wealth of results over the last decade has demonstrated the virtues of incorporating 2D materials, including and especially graphene oxide (GO), to reduce fluid permeability in composite barrier materials. Motivated by several exciting but seemingly inconsistent results in the literature on such barrier materials, in this talk, we highlight the importance of a previously underappreciated factor that can play a surprisingly large role in fluid permeability, namely, the interlayer spacing of the 2D inclusions (which can be affected by fluid initially imbibed within the material as well as flexibility and surface functionalization of the 2D materials, amongst other factors). In support of our claims, we have performed moleculardynamics (MD) simulations that study the influence of interlayer spacing on fluid permeability across a range of systems with varying geometries and driving forces. Based upon our MD results, we construct a nonequilibrium phase map that identifies conditions corresponding to effective barrier behavior. 
Thursday, March 17, 2022 9:24AM  9:36AM 
S11.00008: Breakdown of the StokesEinstein relation for a passive tracer in an oddviscous chiral active fluid Anthony R Poggioli, David T Limmer Isotropic Newtonian fluids in twodimensions may in general exhibit both the typical viscous shear response as well as a socalled odd viscosity, which couples forcing to flow in an orthogonal direction. This antisymmetry reflects the breaking of microscopic timereversal symmetry, either due to activity of the constituent particles or the presence of an external magnetic field. Passive tracer particles suspended in oddviscous fluids experience an anomalous lift force when subjected to a constant velocity, corresponding to nonvanishing offdiagonal components of the mobility tensor and the breakdown of the StokesEinstein relation. We present theoretical results characterising the oddviscous response in active chiral fluids and the mobility tensor of a passive tracer suspended in a such a fluid. Our analytical results are derived using a combination of the pathintegral approach to response in nonequilibrium systems and constrained Gaussian field theory, and they are valid for arbitrary Péclet number. We validate our theoretical results with molecular dynamics simulations of a weakly interacting fluid of rotating active dumbbells. 
Thursday, March 17, 2022 9:36AM  9:48AM 
S11.00009: Propagating high stress fronts, fluid migration and concentration variations in shear thickening cornstarch suspensions. Jeffrey S Urbach, Joia Miller, Vikram Rathee, Daniel L Blair Rheological measurements of dense suspensions often reveal dramatic shear thickening, but only provide measurements of average quantities. Evidence is accumulating that shear thickening is associated with large spatiotemporal fluctuations. Here we describe direct measurements of spatially resolved stress at the boundary of a sheared cornstarch suspensions, showing persistent regions of high local stress that propagate in the flow direction. The persistence of these regions enables a detailed description of their structure, including the profile of boundary stress, dramatic nonaffine velocity of particles at the boundary of the suspension, and a measurement of the relative flow between the particlute phase and the suspending fluid, indicating that the fronts are associated with substantial variations in the concentration of the particulate phase. The propagating fronts fully account for then increase in viscosity with applied stress reported by the rheometer. 
Thursday, March 17, 2022 9:48AM  10:00AM 
S11.00010: Surfing on the order parameter: nanoparticle transport in liquid crystal solvents Linda S Hirst, Alauna Wheeler, Devika Gireesan Sudha, Tom Shneer, Timothy J Atherton Although liquid crystal fluids are well known for their applications in display technologies, they can also be considered as interesting anisotropic solvents for small molecules and nanoparticles. By matching solute lengthscales to the approximate size of the liquid crystal molecules, atypical transport phenomena can be observed that may lead to new selfassembly mechanisms. Such phenomena include steric solubility effects – shape dependent transport in the anisotropic liquid crystal environment – and nanoparticle interactions with topological defects in the liquid crystal phase. In this talk I will review recent progress from our group in this field, including high speed video imaging and analysis of the isotropic to nematic phase transition, and new theoretical approaches to modeling this composite system. Connections with theoretical modelling incorporating anisotropic diffusion and active transport by the isotropic/nematic interface will also be discussed. 
Thursday, March 17, 2022 10:00AM  10:12AM 
S11.00011: Nanoparticle dynamics in semidilute polymer solutions: rings versus linear chains Shivraj Bhagwatrao Kotkar, Ryan PolingSkutvik, Michael P Howard, Arash Nikoubashman, Jacinta C Conrad, Jeremy C Palmer Understanding the dynamics of nanoparticles in polymer solutions is important for applications in drug delivery and enhanced oil recovery. The dynamics of nanoparticles deviate from the generalized StokesEinstein relation when the size of nanoparticles and polymers are comparable as the polymer solution cannot be treated as a homogeneous medium. Dynamics of nanoparticles in semidilute solutions of ring and linear polymers are studied using coarsegrained hybrid molecular dynamics–multiparticle collision dynamics simulations to capture hydrodynamic interactions. The longtime diffusion coefficients of the nanoparticles follow the predictions of a polymer coupling theory by Cai et al., Macromolecules 44, 7853–7863 (2011). At intermediate time scales, the subdiffusive exponents of nanoparticles are strongly correlated to those of the polymer centerofmass for both rings and linear chains and deviate from coupling theory. Hence, the nanoparticle dynamics are strongly coupled to the polymer centerofmass motions for both architectures rather than to their segmental dynamics. The presence of ring concatenations slightly reduces the subdiffusive exponents of the nanoparticles and the polymer center of mass, but the longtime diffusivity of the nanoparticles remains almost constant. 
Thursday, March 17, 2022 10:12AM  10:24AM 
S11.00012: The spreading and splashing of graphene oxide dispersions Jennifer A Quirke, Matthias E Mobius The impact of Newtonian fluid droplets on a solid surface has been extensively studied but much remains to be understood for the splashing and spreading of nonNewtonian fluids. We experimentally study the splashing and spreading behavior of nonNewtonian colloidal suspensions of graphene oxide, a high aspect ratio 2D nanoparticle, in an ethanolwater mixture. Graphene oxide suspensions are shear thinning and exhibit yield stress behavior at higher concentrations. Recent studies on some weakly shear thinning fluids have shown that the existing Newtonian models can predict whether these fluids will splash or spread on a solid surface for a given impact velocity. For higher concentrations of graphene oxide suspensions, we have observed deviations from the predicted splashing behavior. We also examine the spreading behavior of the suspensions on a solid surface, exploring how the maximum spreading ratio of 2D nanoparticle suspension droplets changes with impact velocity and particle concentration. 
Thursday, March 17, 2022 10:24AM  10:36AM 
S11.00013: Peeling tape as a reactiondiffusion system Keisuke Taga, Yoshihiro Yamazaki When the adhesive tape is peeled, twotype structures appear at the peeling front depending on how fast the tape is peeled. In particular, at a critical peeling speed, the two structures switch chaotic, and the peeled trace shows Sierpinskigasket like fractal pattern [1]. 
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