Particle thermophoresis in liquids

We present a microscopic description of thermophoretic phenomena in dilute suspensions of spherical colloids. The specific particle/solvent interfacial interactions generate a force density field F on the surrounding fluid which in turn gives rise to an "effective force" on the colloid. In our approach, such a force turns out to be solely related to the non-conservative anisotropic contribution to F brought forth by the thermal gradient. By adopting a Smoluchowski picture of colloid motion, we find a general expression for the Soret coefficient S(T), which we apply to the specific cases of neutral colloids in pure solvent and of Debye-Hückel systems. For the latter, our result for S(T) agrees with those obtained by previous hydrodynamic approaches.