Bulletin of the American Physical Society
73rd Annual Meeting of the APS Division of Fluid Dynamics
Volume 65, Number 13
Sunday–Tuesday, November 22–24, 2020; Virtual, CT (Chicago time)
Session P08: Suspensions: Rheology (3:10pm - 3:55pm CST)Interactive On Demand
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P08.00001: Universal correlation between jamming distance and shear-thickening strength in dense colloidal suspensions Shravan Pradeep, Alan R Jacob, Lilian Hsiao Tuning shear-thickening in dense suspensions is of great interest owing to its applications in soft robotics, impact armor and industrial manufacturing. Shear-thickening strength ($\beta )$, measured from slope of viscosity-stress flow curve, estimates how fast the suspension viscosity increases with applied shear rate. In this work, we show that prior knowledge of suspension jamming point ($\varphi_{\mathrm{J}})$ will solely predict the $\beta $ parameter in spherically-symmetric colloidal suspensions. In this study, we use smooth and rough poly(methyl methacrylate) colloids with diameters ranging from 0.98 -- 1.82 microns. We found that the sheared rough suspensions shear-thicken earlier and has a lower $\varphi_{\mathrm{J}}$ compared to their smooth counterparts. We incorporate experimentally obtained scalings of the contact number deficit with respect to the distance from jamming ($\Delta \varphi )$ into the mean--field description proposed by Wyarts {\&} Cates (\textit{PRL, 2014}) to predict the flow curves and compare them with experimental results. Our results suggests that there is a universal behavior in the change of $\beta $ parameter from strong (\textgreater 0.9) to weak (\textless 0.7) mode below the value of $\Delta \varphi $/$\varphi_{\mathrm{J}}=$0.1, which is supported by experiments and simulations of similar Brownian systems from the literature. [Preview Abstract] |
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P08.00002: Shear Flow of Suspensions over Porous Media Models Maryam Bagheri, Parisa Mirbod The present work investigates flow of suspensions via rheological methods with the presence of porous media. Examining of how these two systems interact with one another; a series of simple shear flow experiments has been performed using rheometer with parallel plate geometry. The velocity, slip velocity, and slip length with the existence of porous wall have been obtained and characterized in detail. The impact of different fluid concentration ranging from 0 to 40{\%} has been studied, considering two different porous microstructures which have precisely been fabricated in a micron scale on a silicon wafer by a photolithography and deep reactive ion etching. In the first porous model, particles penetrate the porous media, while in the other one the particles do not penetrate into the porous layer. Porosity of both porous mediums is constant at 0.7, while they have various permeabilities. Discontinuity of shear stress at the boundary of porous and free-fluid region has been properly considered and compared to the theoretical prediction of simple shear flow of suspensions. [Preview Abstract] |
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P08.00003: Weakly adhesive suspension shows rate-dependence in oscillatory but not steady shear flows Zhouyang Ge, Raffaella Martone, Luca Brandt, Mario Minale We report rheological measurements of a noncolloidal particle suspension in a Newtonian solvent at 40% solid volume fraction. An anomalous, frequency-dependent complex viscosity is found under oscillatory shear (OS) flow, whereas a constant dynamic viscosity is found under the same shear rates in steady shear (SS) flow. We show that this contradiction arises from the underlying microstructural difference between OS and SS, mediated by weak interparticle forces. Discrete element simulations of proxy particle suspensions confirm this hypothesis and reveal an adhesion-induced, shear thinning mechanism with a -1/5 slope, only in OS, in agreement with experiments. [Preview Abstract] |
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P08.00004: Rheological Measurements in Moderate-Reynolds-Number Liquid-Solid Flows Yichuan Song, Melany Hunt Prior studies on the rheology of suspensions typically cover flows in which the Reynolds numbers are less than 1; limited prior work by Koos {\emph{et al.}} (2012) and Linares {\emph{et al.}} (2017) focus on Reynolds numbers above 10. The current study focuses on experiments for moderate Reynolds numbers where both viscous and inertial effects are important ($Re$ from $0.6$ to $800$). The rheological experiments for both neutrally buoyant and settling suspensions (density ratio of 1 to 1.05) include torque measurements of relatively large SAN and polystyrene particles (mm scale) with solid fractions from 10\% to 50\%, as well as flow visualization and bed expansion measurements. At Stokes numbers higher than 10, particle collisions in the flows become important and contribute to the measured torque. Results show an increased dependence of effective viscosity on the shear rate. \\ [Preview Abstract] |
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P08.00005: Rheological properties of flexible fiber suspensions in the presence of spherical bodies Vahid Tavanashad, Kourosh Shoele Hydrodynamic interaction between flexible fibers and surrounding fluid and fibers interaction with other immersed objects is a key problem in many environmental and industrial applications. In this work, we represent the fibers by a discrete set of points forming a curve (one-dimensional bodies) and use the immersed boundary method to simulate the fluid-structure interaction. We first present the results from the simulation of suspensions of flexible fibers in a cubic domain. It is discussed that the presence of fibers modifies the rheological properties (viscosity) of the suspension. Then we assume different fractions of immersed bodies are three-dimensional spherical objects and investigate how the behavior of suspended immersed bodies is modified with the ratio of fibers to spherical bodies. Since the drag force on the immersed object is a function of the viscosity of the surrounding fluid/suspension, the presence of flexible fibers and their interaction with other suspended objects affects the clustering properties of the assembly and ensemble properties of the system. Finally, a stress closure model is proposed using the homogenization technique to account for the rheological behavior changes with the fiber-to-sphere ratio. [Preview Abstract] |
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P08.00006: Shear Thickening in Bidisperse Dense Suspensions. Nelya Akhmetkhanova, Jeffrey F. Morris, Bulbul Chakraborty Concentrated suspensions often demonstrate striking phenomena such as discontinuous shear thickening (DST) and shear jamming. Despite the increased interest in suspensions at and near these special flow conditions, bidispersity has not been well-studied for DST. We use a simulation model which accounts for short-range lubrication forces, frictional interaction and repulsion between particles, that has shown to successfully reproduce the essential rheological features of DST for nearly monodisperse suspensions. In this work we investigate bidispersity focusing on large to small particle size ratio up to 4, and fraction of large particles. We demonstrate that the rate-dependent suspension viscosity displays a significant reduction, going from discontinuous shear thickening to continuous shear thickening, as particle size ratio becomes larger. Furthermore, under low shear rate conditions the viscosity demonstrates a surprisingly gradual decrease as large particle fraction increases. We show that the observed behavior may be linked to particles undergoing ordering where they are arranged in layers that easily slip past each other.. [Preview Abstract] |
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P08.00007: Rheology of a dilute suspension of active particles with orientation-dependent activity William Uspal, Ruben Poehnl Suspensions of self-motile particles can exhibit rich rheological properties, including “superfluidity,” owing to the injection of energy into the system at the scale of a single particle. Chemically active colloids self-propel by catalyzing the decomposition of molecular "fuel" available in the surrounding solution. In the presence of chemical gradients, or if the catalysis depends on incident light, the chemical activity of the particle will depend on orientation with respect to an external field. This orientation dependence opens new possibilities for designing active fluids with field-tunable rheology. Here, we develop a theoretical framework for computing the rheological properties of a dilute suspension of such particles. In particular, we present theoretical expressions for the stresslet of a chemically active particle, and compute the ensemble-averaged stresslet for various scenarios with field-dependent activity. [Preview Abstract] |
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P08.00008: Controlling dense suspension flows through particle solvation Michael van der Naald, Grayson Jackson, Heinrich Jaeger Dense suspensions often exhibit non-Newtonian flow behaviors such as shear thinning at low applied stresses followed by a transition to shear thickening at higher stresses.~ While recent work has shown that both shear thinning and thickening can be tuned by independently manipulating solvent identity or particle surface chemistry, a holistic understanding of these intertwined factors and its corresponding effect on flow behavior is lacking. We report the steady state rheology of silica particles as a function of solvent molecular weight (MW) and surface chemical functionalities. We find that the shear thinning, shear thickening, and the stress-dependent transition between these two regimes is highly sensitive to both solvent MW and particle surface chemistry. Our results demonstrate that these two factors conspire to control particle surface solvation, which is what ultimately controls the flow behavior of dense suspensions. [Preview Abstract] |
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P08.00009: Viewing stress-activated frictional constraints and shear thickening of dense suspensions through the lens of particle surface chemistry Abhinendra Singh, Grayson L. Jackson, Michael van der Naald, Juan J. de Pablo, Heinrich M. Jaeger The mechanism of shear thickening in dense suspensions has been linked to a stress-controlled transition from unconstrained lubricated (“frictionless”) to constrained unlubricated (“frictional”) rheology. However, it is unclear how these constraints are affected by particle surface chemistry. We show that simulations incorporating reasonable values of sliding friction with a small amount of rolling friction can collapse experimental data covering orders of magnitude in particle size and different particle-fluid chemistries simply by scaling the onset stress for shear thickening. Still, there are notable exceptions where enhanced hydrogen bonding between particles decreases the jamming volume fraction in a manner analogous to sticky or rough particles, which can only be modelled using higher rolling and/or sliding friction coefficients. These observations thus connect the stress-activated formation of hydrogen bonds at the particle surface to rolling and sliding constraints and macroscopic shear thickening behavior. [Preview Abstract] |
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P08.00010: Directed self-assembly of dielectrically polydisperse nanoparticle suspensions into cohesive hierarchical patterns. Suchandra Das, Shriram Pillapakkam, Naga Musunuri, Islam Benouaguef, Edison Amah, Ian Fischer, Pushpendra Singh We show in this work that the inherent dielectric anisotropy of polydisperse suspensions consisting of positively and negatively polarizable nanoparticles can be exploited to guide their self-assembly into a range of hierarchically connected patterns by applying an external electric field. The assembly is driven by inter-particle forces which can be tailored by selecting suitable parameter values, such as the number and size ratios and the polarizabilities of positively and negatively polarizable particles, so that when the electric field is switched on the neighboring particles spontaneously rearrange relative to one another and come together to form cohesive patterns in which particles attract their nearest neighbors. [Preview Abstract] |
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