2008-11-12
10:30 at HCI J 574

Further insights in Soft Matter

Roberto Piazza

Dipartimento di Chimica, Materiali e Ingegneria Chimica “Giulio Natta”, Politecnico di Milano.

I shall discuss some topics which are of current interest in our lab, lingering in particular over the opportunity that these investigations yield to scrutinize basic aspects of equilibrium and non equilibrium statistical physics. More specifically: -- A) I shall show that the analysis of the equilibrium and kinetic sedimentation profiles induced by gravity settling is an efficient route to obtain the equation of state of a colloidal suspension, to inspect fine details of its phase diagram, to provide information on the elastic properties of metastable phases, and to extract relevant information on hydrodynamic forces. In particular, I shall present some recent results on sedimentation of “sticky” hard-spheres, where attractive (“depletion”) forces are induced by the presence of nonionic or charged surfactants. Eventually, sedimentation experiments may yield crucial information on the physical origin and nature of gel and glassy phases. -- B) I shall discuss thermophoresis, a particularly puzzling non equilibrium transport phenomenon, which basically consists in particle drift induced by a thermal gradient. Thermophoresis can be profitably exploited in separation and fractionation methods, in particular using microfluidic devices: yet, the microscopic mechanisms underlying this effect are still partly understood. Here I shall review the experimental evidences on colloid thermophoresis collected by our group on a large class of colloid and macromolecular systems, ranging from micellar solutions to polymers, microemulsions, proteins, latex particles. These results have allowed us to extract basic ideas about the origins of thermally-driven particle transport, and to build up a tentative general hydrodynamic model of thermophoresis.