The microstructure of a strongly coupled liquid undergoing a shear flow was studied experimentally. The liquid was a shear melted two-dimensional plasma crystal, i.e., a single-layer suspension of micrometer-size particles in a rf discharge plasma. Trajectories of particles were measured using video microscopy. The resulting microstructure was anisotropic, with compressional and extensional axes at around $\pm 45^{\circ}$ to the flow direction. Corresponding ellipticity of the pair correlation function $g({\bf r})$ or static structure factor $S(\bf{k})$ gives the (normalized) shear rate of the flow.
Dissipation and microstructure in sheared active suspensions of squirmers
School of Advanced Manufacturing Engineering, Nanjing University（南京大学高级制造工程学院）；Department of Mechanical Engineering and Institute of Applied Mathematics, University of British Columbia（不列颠哥伦比亚大学机械工程系与应用数学研究所）
We explore the rheology predicted by a recently proposed constitutive model for jammed suspensions of soft elastic particles derived from particle-level dynamics [Cuny et al., Phys. Rev. Lett. 127, 218003 (2021)]. Our model predicts that the orientation of the anisotropy of the microstructure, governed by an interplay between advection and contact elasticity, plays a key role at yielding and in flow. It generates normal stress differences contributing significantly to the yield criterion and Trouton ratio. It gives rise to non-trivial transients such as stress overshoots in step increases of s…
Under inhomogeneous flow, dense suspensions exhibit complex behaviour that violates the conventional homogenous rheology. Specifically, one finds flowing regions with a macroscopic friction coefficient below the yielding criterion, and volume fraction above the jamming criterion. We demonstrate the underlying physics by incorporating shear rate fluctuations into a recently proposed tensor model for the microstructure and stress, and applying the model to an inhomogeneous flow problem. The model predictions agree qualitatively with particle-based simulations.
For applications of pulmonary surfactant delivery to the lungs, the question of rheology of the existing clinical formulations is of upmost importance. Recently, Ciutara and Zasadsinky (Soft Matter, 2021, 17, 5170-5182) measured the rheological properties of Infasurf, Survanta and Curosurf, three of the most used pulmonary surfactant substitutes. This study revealed that these fluids are shear-thinning and characterized by a yield stress. The results obtained by Ciutara et al. on Curosurf differ from our results published in Colloids and Surfaces B: Biointerfaces, 2019, 178, 337-345 and in ACS…
Visualizing shear-induced structures in carbon black gels by tomo-rheoscopy
ENSL, CNRS, Laboratoire de physique（ENS-Lyon, 法国国家科学研究中心, 物理实验室）；Department of Materials, ETH Zürich（苏黎世联邦理工学院材料系）；Université Claude Bernard Lyon 1, CNRS, Institut Lumière Matière, UMR5306（里昂第一大学, 法国国家科学研究中心, 光物质研究所）；Swiss Light Source, Paul Scherrer Institut（瑞士光源, 保罗谢尔研究所）；Leibniz Universität Hannover（汉诺威莱布尼茨大学）；International Research Laboratory, French American Center for Theoretical Science, CNRS, KITP, Santa Barbara（国际研究实验室, 法美理论科学中心, 法国国家科学研究中心, 加州大学圣塔芭芭拉分校卡弗里理论物理研究所）
We develop a tensorial constitutive model for dense, shear-thickening particle suspensions subjected to time-dependent flow. Our model combines a recently proposed evolution equation for the suspension microstructure in rate-independent materials with ideas developed previously to explain the steady flow of shear-thickening ones, whereby friction proliferates among compressive contacts at large particle stresses. We apply our model to shear reversal, and find good qualitative agreement with particle-level, discrete-element simulations whose results we also present.
A fundamental challenge for disordered solids is predicting macroscopic yield from the microscopic arrangements of constituent particles. Yield is accompanied by a sudden and large increase in energy dissipation due to the onset of plastic rearrangements. This suggests that one path to understanding bulk rheology is to map particle configurations to their mode of deformation. Here, we perform laboratory experiments and numerical simulations that are designed to do just that: 2D dense colloidal systems are subjected to oscillatory shear, and particle trajectories and bulk rheology are measured.…
Dusty plasmas represent a powerful playground to study the collective dynamics of strongly coupled systems with important interdisciplinary connections to condensed matter physics. Due to the pure Yukawa repulsive interaction between dust particles, dusty plasmas do not display a traditional liquid-vapor phase transition, perfectly matching the definition of a supercritical fluid. Using molecular dynamics simulations, we verify the supercritical nature of dusty plasmas and reveal the existence of a dynamical liquid-like to gas-like crossover which perfectly matches the salient features of the …
Univ Lyon, Ens de Lyon, CNRS, Laboratoire de Physique（里昂大学、巴黎高等师范学校里昂分校、法国国家科学研究中心、物理实验室）；Department of Polymer Engineering, IPC, University of Minho（米尼奥大学高分子工程系）
Shear history plays an important role in determining the linear and nonlinear rheological response of colloidal gels and can be used for tuning their structure and flow properties. Increasing colloidal particle aspect ratio lowers the critical volume fraction for gelation due to an increase of the particle excluded volume. Using a combination of rheology and confocal microscopy we investigate the effect of steady and oscillatory pre-shear history on the structure and rheology of colloidal gels formed by silica spheres and rods of length L and diameter D (L/D = 10) dispersed in 11 M CsCl soluti…
The shear-induced self-organization of active rotors into stripy aggregates is studied by carrying out computational simulations. The rotors, modeled by monolayers of frictional spheres, develop to stripy microstructures only when they counterrotate with respect to the vorticity of the imposed shear flow. The average width of the stripes is demonstrated to be linearly dependent on the relative intensity of active torque to the shear rate. By giving insight into three collective particle behaviors, i.e., shear-induced diffusion, rotation-induced rearrangement, and edge flows, we explain the mec…
Colloidal gels are out of equilibrium soft solids composed of attractive Brownian particles that form a space-spanning network at low volume fractions. The elastic properties of these systems result from the network microstructure, which is very sensitive to shear history. Here, we take advantage of such sensitivity to tune the viscoelastic properties of a colloidal gel made of carbon black nanoparticles. Starting from a fluidized state under an applied shear rate $\dot γ_0$, we use an abrupt flow cessation to trigger a liquid-to-solid transition. We observe that the resulting gel is all the m…
Oscillatory shear has been widely used to study the rheological properties of suspensions under unsteady shear. Furthermore, recent works have shown that oscillatory flows can improve the flowability of dense suspensions. While most studies have been done under constant volume we here study oscillatory shear flows of a two-dimensional suspensions using a normal pressure-controlled set-up. To characterise the rheology, we introduce both a complex macroscopic friction coefficient $μ^{*}$, following the convention of the complex viscosity $η^{*}$, and a shear-rate averaged viscous number $J'$. Th…
To elucidate the key factor for the quantitative prediction of the shear-thickening in suspensions in viscoelastic fluids, direct numerical simulations of many-particle suspensions in a multi-mode Oldroyd-B fluid are performed using the smoothed profile method. Suspension flow under simple shear flow is solved under periodic boundary conditions by using Lees--Edwards boundary conditions for particle dynamics and a time-dependent oblique coordinate system that evolves with mean shear flow for fluid dynamics. Semi-dilute many-particle suspensions up to a particle volume fraction of 0.1 are inves…
The rheological behaviors of suspension of ideally conductive particles in an electric field are studied using large-scale numerical simulations in the limit of zero-shear-rate flow. Under the action of an electric field, the particles undergo the nonlinear electrokinetic phenomenon termed as dipolophoresis, which is the combination of dielectrophoresis and induced-charge electrophoresis. For ideally conductive particles, the dynamics of the suspension are primarily controlled by induced-charge electrophoresis. To characterize the rheological properties of the suspension, the particle stress t…
