Résumé
We use novel space and time resolved light scatterering methods to investigate the dynamics of colloidal suspensions under gravitational stress. In the first part of my talk, I'll discuss the behavior of colloidal gels, where the volume fraction is moderate (phi~0.05-0.2) and attractive interactions are induced via the depletion mechanism. I'll show that a single parameter, the time dependent compressive strain rate, rules both the macroscopic settling of the gel and its microscopic dynamics [1]. Additionally, gels prepared at various volume fractions and interaction strength exhibit a universal beahvior in that their asymptotic concentration profile can be scaled onto a master curve [2]. In the second part of my talk, I'll discuss nearly neutrally boyant suspensions of colloidal spheres, to which small amounts of fast-settling probe spheres are added. The focus will be on the volume fraction dependence of the suspension viscosity and its relationship with the structural relaxation time. [1] G. Brambilla, S. Buzzaccaro, R. Piazza, L. Berthier, L. Cipelletti, Highly nonlinear dynamics in a slowly sedimenting colloidal gel, Phys. Rev. Lett. 106, 118302 (2011) [2] S. Buzzaccaro, E. Secchi, G. Brambilla, R. Piazza and L. Cipelletti, Equilibrium concentration profiles and sedimentation kinetics of colloidal gels under gravitational stress, J. Phys.: Condens. Matter 24 284103 (2012)