Free-Surface Instability and Stratification of Critical Microemulsions

We have studied the influence of temperature gradients on the concentration distribution in a microemulsion near a consolute critical point. Temperature inhomogeneities much smaller than the distance to the critical temperature trigger convective flows along the free surface (liquid-vapour interface) and are the cause of a considerable stratification of the bulk sample. All these phenomena disappear if the vapour phase on top of the sample is replaced by a solid phase. We propose an explanation involving a thermodiffusion-induced superficial concentration gradient and the resulting Marangoni convection.