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Masaki Sano: „Tunable Soret effect of colloidal particles by a nonequilibrium depletion”
University of Tokyo, Japan

We studied a novel nonequilibrium phenomenon of colloids in polymer solution. The nonequilibrium distribution of colloids in a polymer solution under a temperature gradient is studied experimentally. A slight increase of local temperature by a focused laser drives the colloids towards the hot region, resulting in the trapping of the colloids irrespective of their own thermophoretic properties. An amplification of the trapped colloid density with the polymer concentration is measured, and is quantitatively explained by hydrodynamic theory. The origin of the attraction is a migration of colloids driven by a nonuniform polymer distribution sustained by the polymer’s thermophoresis. These results show how to control the thermophoretic properties of colloids and provide a new micromanipulation.