Résumé:

We study the fingering instability of the interface between two miscible fluids, a colloidal suspension and its own solvent [1]. The temporal evolution of the interface in a Hele-Shaw cell is found to be governed by the competition between the nonlinear viscosity of the suspension and an off-equilibrium, effective surface tension $\Gamme_e$. By studying suspensions in a wide range of volume fractions, $\Phi_C$, we show that $\Gamma_e ∼ \Phi_C^2$, in agreement with Korteweg’s theory for miscible fluids. The surface tension exhibits an anomalous increase with particle size, which we account for using entropy arguments. [1] Truzzolillo et al, Phys. Rev. Lett 112, 128303 (2014).