Stress Contributions in Colloidal Suspensions: The Smooth, the Rough, and the Hairy.

The collective properties of colloidal suspensions, including their rheology, reflect an interplay between colloidal and hydrodynamic forces. The surface characteristics of the particles play a crucial role, in particular, for applications in which interparticle distances become small, i.e., at high concentrations or in aggregates. In this Letter, we directly investigate this interplay via the linear viscoelastic response of the suspensions in the high-frequency regime, using particles with controlled surface topographies, ranging from smooth to hairy and rough particles. We focus directly on the stresses at the particle level and reveal a strong impact of the surface topography on the short-range interactions, both dissipative and elastic. As the particle topography becomes more complex, the local stresses depend on how the topography is generated. The findings in this Letter, in particular, show how changes in topography can both screen or enhance the dissipation, which can be used to engineer the properties of dense or aggregated suspensions.