Discontinuous shear-thinning in adhesive dispersions

We present simulations for the steady-shear rheology of a model adhesive dispersion in the dense regime. We vary the range of the attractive interparticle forces u as well as the strength of the dissipation b. For large dissipative forces, the rheology is governed by the Weissenberg number Wi similar to b(gamma) over dot / u and displays Herschel-Bulkley form sigma = sigma(y) + cWi(v) with exponent v = 0.45. Decreasing the strength of dissipation, the scaling with Wi breaks down and inertial effects show up. The stress decreases via the Johnson-Samwer law Delta sigma similar to T-s(2/3), where temperature T-s is exclusively due to shear-induced vibrations. During flow, particles slide past each other such that their relative velocities are primarily directed tangentially to the particle surfaces. This tangential channel of energy dissipation and its suppression leads to a discontinuity in the flow curve and an associated discontinuous shear-thinning transition. We set up an analogy with frictional systems, where the phenomenon of discontinuous shear-thickening occurs. In both cases, tangential forces, frictional or viscous, mediate a transition from one branch of the flow curve with low tangential dissipation to one with larger tangential dissipation.