Pattern formation without heating in an evaporative convection experiment

We present an evaporation experiment in a single fluid layer reproducing conditions of volatile fluids in nature. When latent heat associated to the evaporation is large enough, the heat flow through the free surface of the layer generates temperature gradients that can destabilize the conductive motionless state giving rise to convective cellular structures without any external heating. Convective cells can be then observed in the transient range of evaporation from an initial depth value to a minimum threshold depth, after which a conductive motionless state appears until the evaporation finishes with an unwetting sequence. The sequence of convective patterns obtained here without heating is similar to that obtained in Benard-Marangoni convection. This work presents the sequence of spatial bifurcations as a function of the layer depth. The transition between square-to-hexagonal pattern, known from non-evaporative experiments, is obtained here with a similar change in wavelength.