Particle dispersion in sheared suspensions: Crucial role of solid-solid contacts

We performed high resolution measurements of the dynamics of non-Brownian and neutrally buoyant particles subjected to a periodic shear flow under low Reynolds number conditions. By changing the particle roughness and showing that it significantly affects the particle motion, we provide direct evidence that particle solid-solid contacts occur in viscous suspensions and strongly influence the particle dynamics. An accurate prediction of the particle trajectories is obtained with a minimal model that solely includes normal lubrication interactions and a frictionless contact force.