Résumé:

We report on experiments probing the interface between two miscible fluids, an aqueous suspension of submicron colloidal particles and water. The suspension is confined between two plates and water is injected through a small hole in the top plate. As water is pushed through the more viscous colloidal suspension, the interface between the two fluids is destabilized, forming distinctive patterns similar to those observed for immiscible fluids (see figure below). We show that the interface shape is ruled by an off-equilibrium surface tension and validate quantitatively the one-century-old predictions by Korteweg. These findings open the way to a better understanding of a wealth of phenomena, from crystal nucleation and growth to shaping and forming in material science.