Thermophoresis is particle drift induced by a temperature gradient. By measuring the full temperature dependence of this effect for polystyrene latex suspensions, we show that the thermophoretic mobility (or “thermal diffusion coefficient”) $D_T$ is basically independent on particle size, in particular, when the interfacial properties of the colloidal particles are carefully standardized by adsorbing a surfactant layer on the particle surface. Even more, all investigated systems show values of $D_T$ which are very close to those measured for simple micellar solutions of the adsorbed surfactant. Our findings could be of relevance for downsizing microfluidics to the nanometric range.

Thermophoresis is particle motion induced by thermal gradients. Akin to other nonequilibrium transport processes such as thermal diffusion in fluid mixtures, it is both experimentally and theoretically a challenging subject. New insights stemming from careful experimental surveys and strict theoretical models have however shed light on the underlying physical mechanisms, enabling depiction of thermophoresis as a subtle interfacial effect. These recent advancements open up alluring perspectives to exploit thermophoresis as a novel tool in macromolecular fractionation, microfluidic manipulation, and selective tuning of colloidal structures.