Barth, Anna - Cornell University

Universal scaling of shear thickening suspensions under acoustic perturbation

Nearly all dense suspensions undergo dramatic and abrupt thickening transitions in their flow behavior when sheared at high stresses. Such transitions occur when suspended particles come into frictional contact with each other to form structures that resist the flow. These frictional contacts can be disrupted with acoustic perturbations, thereby lowering the suspension’s viscosity. Acoustic perturbations offer a convenient way to control the suspension’s shear thickening behavior in real time, as the suspension responds to the perturbation nearly instantaneously. Here, we fold these acoustic perturbations into a universal scaling framework for shear thickening, in which the viscosity is described by a crossover scaling function from the frictionless jamming point to a frictional shear jamming critical point. We test this theory on sheared suspensions with acoustic perturbations and find experimentally that the data for all shear stresses, volume fractions, and acoustic powers can be collapsed onto a single universal curve. Within this framework, a scaling parameter that is a function of stress, volume fraction and acoustic power determines the proximity of the system to the frictional shear jamming critical point and ultimately the viscosity. Our results demonstrate the broad applicability of the scaling framework, its utility for experimentally manipulating the system, and open the door to importing the vast theoretical machinery developed to understand equilibrium critical phenomena to elucidate fundamental physical aspects of the non-equilibrium shear thickening transition.