Sliding drops on soft substrates*

Drops sliding onto viscoelastic substrates dissipate energy in both liquid and solid. So far, studies focused on substrates much more viscous than liquids. In accordance with recent theoritical predictions, we assume dissipation ratio between solid and liquid is a key parameter of soft wetting systems. We conducted sliding experiments onto thick viscoelastic substrates and changed the dissipation ratio increasing liquid viscosity. A huge dissipation in the solid rises an apparent hysteretic behaviour, which confirms theoretical predictions; this so called “soft hysteresis” results in longer drops. Increasing dissipation in the solid also changes the relation between weight and running speed. Thus, we experimentally showed that dissipation ratio controls dynamical soft wetting systems. This key parameter could optimise liquid runoff processes such as dew collectors.