Spreading of viscous drops on a liquid-infused solid

Textured materials infused by oil, also known as liquid-infused solids (LIS), have special dynamical properties, in particular, because the liquid trapped in the texture lends them liquid-like properties with very little adhesion towards water and the possibility to promote slip. We revisit the classical problem of spreading of a droplet (water or glycerol), but on these special surfaces that are hemi-solid, hemi-liquid. We observe that a millimetric water drop spreading on a LIS (typically in a time scale of 10 milliseconds) is always slower than that on a solid - the more viscous the oil infused, the slower the spreading. Conversely, glycerol drops spread much faster on infused surfaces - the lower the viscosity of the oil, the faster the glycerol drop spreads, and always spreads faster than on a solid. We study experimentally the physics of such unique spreading behaviors and the parameters that govern it.