Experimental Evidence of the Motion of a Single Out-of-Equilibrium Drop

Abstract

We show experimentally that, when a single, neutrally buoyant drop is injected in a binary mixture, either it remains quiescent or it moves, depending on whether or not the composition of the drop and that of the surrounding phase coincide with the equilibrium concentrations. In general, the movement of out-of-equilibrium drops, which is called diffusiophoresis, is induced by the Korteweg body force. This force is proportional to the chemical potential gradient and is therefore non-zero only when the system is in conditions of chemical nonequilibrium. In this letter, we show experimentally that this movement occurs for a single drop as well, even when the initial condition is (almost) isotropic. This instability, although it does not have a complete analytical explanation, has been predicted in the numerical simulations by Vladimirova, Malagoli & Mauri (Phys. Rev. E 1999, 60, 2037)