Drop friction on liquid-infused materials.

We discuss in this paper the nature of the friction generated as a drop glides on a textured material infused by another liquid. Different regimes are found, depending on the viscosities of both liquids. While a viscous drop simply obeys a Stokes-type friction, the force opposing a drop moving on a viscous substrate becomes non-linear in velocity. A liquid on an infused material is surrounded by a meniscus, and this specific feature is proposed to be responsible for the special frictions observed on both adhesive and non-adhesive substrates.