'Thermal forces': colloids in temperature gradients

In the presence of a thermal gradient, macromolecular solutes or dispersed particles drift to the cold or to the hot side: this effect is known as thermophoresis, and is the counterpart of particle suspensions of the Soret effect (or thermal diffusion) in simple fluid mixtures. Here I review recent experimental results on colloid thermophoresis and present new data suggesting a universal nature for the temperature dependence of thermophoresis in aqueous systems. There are strong analogies between thermophoresis in liquids and other thermally induced flow processes like gas thermal creep and membrane thermo-osmosis; starting from these, I present some guidelines for a general model of thermophoresis in disperse systems, accounting both for single-particle and collective effects.