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 S24: Flow of Complex FluidsFocus Live
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Sponsoring Units: DFD Chair: Christopher Browne, Princeton University |
Thursday, March 18, 2021 11:30AM - 12:06PM Live |
S24.00001: Patchy elastic turbulence generates anomalous flow resistance in porous media Invited Speaker: Sujit Datta Diverse applications rely on the viscous-dominated flow of polymer solutions through disordered porous media. For many polymers, the macroscopic flow resistance abruptly increases above a threshold flow rate in a porous medium, but not in bulk solution. The reason for this anomalous increase has remained a puzzle ever since it was first reported over half a century ago. Here, by directly visualizing the flow in a transparent 3D porous medium, we demonstrate that this anomalous increase is due to the added dissipation arising from an elastic instability in which the flow exhibits strong spatio-temporal fluctuations reminiscent of inertial turbulence, despite the vanishingly small Reynolds number. We find that the transition to unstable flow in each pore is akin to a universal second-order phase transition, arising due to the increased persistence of discrete patches of instability above an onset flow rate; however, this onset varies from pore to pore. Thus, unstable flow is patchy across the different pores of the medium. Guided by these findings, we directly link the energy dissipated by patchy pore-scale fluctuations to the anomalous increase in flow resistance through the entire medium. Our work thus helps to resolve the long-standing puzzle of why polymer solutions exhibit an anomalous increase in macroscopic flow resistance in porous media and provides guidelines for predicting and controlling these flows. |
Thursday, March 18, 2021 12:06PM - 12:18PM Live |
S24.00002: Micromixing of non-Newtonian fluids Kira Daher, Ryan Barrett, Mahmud Raihan, Xiangchun Xuan This study examines the micromixing of non-Newtonian fluids through a constriction within a T-shaped microchannel. Previous micro-mixers have been focused mostly on Newtonian fluids, however, many chemical and biologic fluids exhibit non-Newtonian properties. As the use of microfluidic devices to handle fluids for various chemical and biomedical applications increases, the need for micromixer that can handle non-Newtonian fluids is growing. The flow within microchannels is essentially laminar, due to their small size, leading to long mixing times induced by slow molecular diffusion. This study demonstrates that a constriction microchannel can be used to accelerate mixing by employing the fluid rheology-induced flow instability. Specifically, we investigate the micromixing of shear-thinning fluids as well as the micromixing of shear-thinning fluid with water in flows with a range of Reynolds numbers. |
Thursday, March 18, 2021 12:18PM - 12:30PM Live |
S24.00003: Coupling flow directions in emulsions with wall roughness Akankshya Majhi, Lars Kool, Raquel Serial, Joshua Dijksman, Jasper Van der Gucht Dense emulsions behave as a yield stress fluid, that has a critical stress above which the material starts to flow. Typically, the yield stress behaviour is captured in the Herschel-Bulkley model, which assumes a constant yield stress as material parameter. The microscopic origin of the yield stress is still under debate. It can be argued that flow in orthogonal directions simultaneously affect the yield stress and will make the yield stress flow rate or field dependent. Therefore, it is important to understand how two orthogonal flows affect each other and how the Herschel-Bulkley equation can be generalised to explain such orthogonal flow situations. In this work, we show that wall patterning can be used to generate flow in two orthogonal directions that affect each other significantly. We induce secondary flows via shearing a common yield stress fluid in a rheometer using a concentric cylinder geometry with angled ridges. We quantify our results by calibrating the effect of wall roughness through an effective ridge depth. We also image the flow fields by employing rheoMRI methods to show that flow directions in yield stress fluids are indeed significantly coupled. |
Thursday, March 18, 2021 12:30PM - 12:42PM Live |
S24.00004: Coupling of particle ordering and stress fluctuations in shear thickening suspensions revealed by high speed confocal line scan imaging Joia Miller, Daniel Blair, Jeffrey S Urbach Shear thickening suspensions transition from low viscosity to high viscosity or shear jammed states under high stress. While both the bulk rheology and the microscopic driving forces of such transitions are well-studied, the bridge between the microscopic and macroscopic scales is still unclear. Measurements at the boundaries indicate that dynamic high stress regions propagate through shear thickening suspensions of colloidal spheres. Here we use line scans on a confocal microscope to visualize high speed particle flows in a sheared suspension. These measurements reveal that high stress regions are correlated with significant drops in both speed and in local particle order, extending from the boundary many particle diameters deep into the suspension. |
Thursday, March 18, 2021 12:42PM - 12:54PM Live |
S24.00005: Dectection of heterogeneities in a shear thickening suspension through a local normal stress measurement Anais Gauthier, Mickael Pruvost, Annie Colin We study the shear-thickening of a concentrated suspension of non-brownian particles (cornstarch) using an in-house sensor array. The sensor is placed on the bottom plate of a torsional rheometer, and gives access to the pressure on 25 regularly spaced measuring points (of surface 4x4 mm2 each). It is used to map the local normal stresses in the flow. |
Thursday, March 18, 2021 12:54PM - 1:06PM Live |
S24.00006: Mapping the nonlinear stress propagation in topological polymer blends Karthik Peddireddy, Gina Aguirre, Jonathan Garamella, Ryan J. McGorty, Rae M Robertson-Anderson Entangled polymers and blends of varying topologies and stiffnesses exhibit complex nonlinear rheological properties that depend on the blend composition and the scale of the strain. How local nonlinear stresses propagate through these systems remains an open question. Here, we combine optical tweezers microrheology with fluorescence imaging and differential dynamic microscopy (DDM) to map the deformation field arising from a local nonlinear strain in entangled polymer blends. We use optical tweezers to impart local nonlinear strains and measure the resulting stresses during and following strain. We simultaneously image labeled DNA molecules surrounding the strain site and use DDM to determine how the macromolecular dynamics vary with distance from the applied strain. We perform these measurements on entangled solutions of linear and ring DNA, as well as blends of DNA and microtubules. Our approach, which combines active microrheology with macromolecular tracking and differential dynamic microscopy, directly links nonlinear stress propagation to macromolecular deformations and dynamics, and is applicable to a wide range of complex fluids and polymeric materials. |
Thursday, March 18, 2021 1:06PM - 1:18PM Live |
S24.00007: The “Little” Bang: Tracing Bubble Growth Back to Nucleation in Polymer Foaming Andrew Ylitalo, Huikuan Chao, Thomas Fitzgibbons, Sriteja Mantha, Valeriy Ginzburg, Weijun Zhou, Ernesto Di Maio, Richard C Flagan, Zhen-Gang Wang, Julie A Kornfield Bubble nucleation sets the structure of polymer foams well before bubbles grow to their final size, but it is more difficult to measure than growth. Despite the many models of bubble nucleation, they lack experimental validation, often due to the challenge of observing fleeting nanoscopic nuclei. Here, we estimate the nucleation time of bubbles by first modeling their growth after they reach an optically observable size, then extrapolating backwards in time to their expected size at nucleation. We examined bubbles of CO2 in polyol as they underwent a rapid (< 1 s) depressurization from as much as 10 MPa to atmospheric pressure along a custom-built microfluidic channel. Bubbles were recorded with high-speed optical microscopy as short as tens of microseconds after nucleation. We modeled their growth with an Epstein-Plesset model modified to account for depressurization, using thermophysical properties of polyol and CO2 mixtures measured with the Di Maio group (U Naples) as model parameters. We compared our results to predictions of nucleation energy barriers made using the string method applied to density functional theory developed by the Wang group (Caltech). |
Thursday, March 18, 2021 1:18PM - 1:30PM Live |
S24.00008: Numerical modeling of droplet formation for weakly elastic fluids using level set model Hassan Pouraria, Reza Foudazi The significant interest in 3D printing and coating technology requires a more profound knowledge of the complex droplet formation process. The complex topological behavior of capillary-driven thinning and pinch-off during the droplet formation becomes even more complex by adding a minute amount of polymers. The present study aims at modeling the droplet formation of weakly elastic fluids in the dripping regime. To this end, the level set model is employed for interface tracking while an axisymmetric computational domain is used to reduce the computational cost. The Oldroyd-B model is used to take into account the viscoelastic effects. Numerical modeling is conducted for fluids with identical shear viscosity while the elastic properties change. The obtained numerical results are compared against the available experimental data to evaluate the accuracy of the solution. In addition, the influence of the elastic properties of the fluid on the interface evolution is investigated. Furthermore, the transition from the inertio-capillary to the elasto-capillary regime before the pinch-off moment is discussed. |
Thursday, March 18, 2021 1:30PM - 1:42PM Live |
S24.00009: Pinching dynamics, rheology and elastic instabilities of Boger fluids Alexander Kubinski, Fahed Albreiki, Vivek Sharma Boger fluids refer to viscoelastic that exhibit rate-independent shear viscosity. The absence of rate-dependent viscosity allows identification of purely elastic instabilities and comparison with Oldroyd-B model, which is a constitutive model that includes elasticity without allowing for shear thinning. In this study, we investigate the shear and extensional rheology response of Boger fluids to identify the role played by enhancement in solvent viscosity at a fixed polymer concentration. The increase in solvent viscosity and relative contribution of viscous and elastic stresses is contrasted in experiments carried out using~dripping-onto-substrate rheometry, as well as viscoelastic fingering. |
Thursday, March 18, 2021 1:42PM - 1:54PM Live |
S24.00010: Studies on hydrodynamic stability of viscoelastic flows in a Hele-Shaw cell. Prabir Daripa, Zhiying Hai We will present some recent results on the stability of Multi-Layer Hele-Shaw flows of viscoelastic fluids in a Hele-Shaw cell. We will consider displacement studies of one viscoelastic fluid by another one, where either of the fluids can be upper-convected Maxwell, Oldroyd-B or Newtonian. This will build on our previous works [1]. We will give refinements of earlier works and present some new results missing in the works of Wilson [2]. |
Thursday, March 18, 2021 1:54PM - 2:06PM Live |
S24.00011: Elastic Turbulence is Spatially Patchy in 3-D Porous Media Christopher Browne, Sujit Datta Polymer solutions are often injected in porous media for applications such as oil recovery and groundwater remediation. As the fluid navigates the tortuous pore space, elastic stresses build up, causing the flow to become unstable at sufficiently large flow rates: a phenomenon often known as “elastic turbulence”. However, what physical factors determine the onset of this instability, and what its spatial and temporal characteristics are, remain unknown. Here, we use direct visualization in model three-dimensional porous media to address this gap in knowledge. We show that the onset of unstable flow in each pore is akin to a second-order phase transition, arising due to the persistence of discrete patches of instability. Thus, unstable flow is patchy across the different pores of the medium. Guided by these findings, we directly link the energy dissipated by pore-scale fluctuations to the flow resistance through the entire medium, enabling prediction of the macroscopic transport behavior. Together, these results reveal the rich array of behaviors that can arise during the unstable flow of polymer solutions through porous media, and provide a general framework by which flow fluctuations can be predicted and controlled. |
Thursday, March 18, 2021 2:06PM - 2:18PM Live |
S24.00012: Nonequilibrium osmotic pressure in sticky-probe active microrheology Derek Huang, Roseanna Zia We present a theoretical study of the influence of interparticle attractions and hydrodynamic interactions on nonequilibrium osmotic pressure in a colloidal suspension via active microrheology, where a Brownian probe driven by external forces through the suspension is tracked to infer rheology. To model this system, we solve a Smoluchowski equation to obtain structure and compute osmotic pressure through statistical mechanics. Attractions decrease equilibrium osmotic pressure and phase-separate a suspension at higher volume fractions when the second virial coefficient is sufficiently negative, B2 ≈ –1/2. Under external forcing, nonequilibrium osmotic pressure evolves nonmonotonically with both attraction and flow strength. We demonstrate that strong hydrodynamic interactions dramatically lower the nonequilibrium osmotic pressure in attractive systems and can even induce negative osmotic pressure in flowing systems, driving flow-induced particle aggregation and potential nonequilibrium phase separation. Our results suggest that detailed knowledge of both attractive and repulsive forces, and of hydrodynamic interactions, enables tuning of tracer particle motion inside sticky environments such as biological fluids and control over aggregation kinetics in self-assembly processes. |
Thursday, March 18, 2021 2:18PM - 2:30PM On Demand |
S24.00013: Fluid rheological effects on polymer solution flows in an expansion-contraction microchannel Mahmud Raihan, Purva Jagdale, Xiangchun Xuan A fundamental understanding of the pore-scale flow dynamics of polymer solutions in porous media benefits applications such as enhanced oil recovery, groundwater remediation and microfluidic particle manipulation. The heterogeneous real-world pores are frequently represented by one or multiple consecutive expansions (i.e., pore body) and contractions (i.e., pore throat) in microfluidic models. We perform a systematic experimental study of the fluid rheological effects on polymer solution flows through a single expansion-contraction microchannel. We investigate the influences of fluid elasticity, shear thinning and inertia at both their individual and different combination levels with five types of common polymer solutions and water. All fluids are tested in a similar wide range of flow rates. The observed flow regimes and vortex developments are summarized in the same dimensionless parameter spaces for a direct comparison. |
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