Solutal convection in confined geometries: enhancement of colloidal transport

We evidence experimentally and theoretically that natural convection driven by solutal density differences in a molecular binary mixture can boost the transport of colloids. We demonstrate that such buoyancy-driven flows have a negligible influence on the gradients that generate them, for moderate Rayleigh numbers in a confined geometry. These flows therefore do not homogenize the binary mixture but can disperse very efficiently large solutes. We illustrate the relevance of such effects thanks to several original experiments: drying of confined droplets, microfluidic evaporation, and interdiffusion in microfluidic flows.