Forced impregnation of a capillary tube with drop impact

We experimentally investigate how the impregnation of porous media can be forced using the initial kinetic energy of an impacting drop. We focus on the scale of a single pore – either hydrophilic or hydrophobic – and thus study the impact of a single drop falling on vertical cylindrical capillary tubes. This experimental configuration therefore differs from the impregnation of a porous media because of the finite volume of the drop and its initial kinetic energy. We observe different limit regimes: at low impact velocity, we recover the classical results for impregnation. The liquid does not impregnate the hydrophobic pore while it is totally sucked into the hydrophilic one. At high impact velocities, the drop is broken in two parts: one part spreads at the top of the surface while an isolated slug is trapped within the pore. We determine the critical speeds for these regimes and obtain a full phase-diagram for our observations. We also stress the characteristics of impregnating slugs namely their volume and their motion within the pores.