Discontinuous shear thickening in dense suspensions:

mechanisms, force networks, and fluctuations

Jeffrey F. Morris

Levich Institute and Dept. of Chemical Engineering

CUNY City College of New York

Dense suspensions of particles in a liquid, with industrial examples including coatings or precursors to solid ceramics and cements, can be quite difficult to process because their flow properties are very sensitive to particle surface interactions. We focus on the extreme rate dependence known as “discontinuous shear thickening” (DST) where the viscosity undergoes a finite and typically large discontinuous jump in viscosity at some shear rate. Simultaneous with DST, there is a large increase in the normal stress, including the nonequilibrium osmotic pressure, or ‘particle pressure’, leading to the historical name of `dilatancy’ for shear thickening. Our computational simulations inclusive of the three ingredients of i) lubrication hydrodynamics, ii) repulsive interparticle forces (e.g. due to surface charge) and iii) contact with friction have been shown to reproduce the primary features of DST found experimentally; this is called lubricated-to-frictional (LF) rheology. We describe the main features of the shear thickening transition in the LF scenario, including the observation of extreme fluctuations. Using our simulation results, we explore the microscopic basis for the LF transition in the force network developed under flow.

Snapshot from shear flow of suspended particles in viscous liquid, with contact forces (including friction) indicated by colored lines of thickness proportional to magnitude.

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