Sliding of liquid droplets on thin viscoelastic soft layers

Soft substrates are deformed by liquid-vapor surface tension upon contact with liquid droplets, forming the well-known wetting ridge. This ridge dynamically propagates with the moving contact line and critically influences liquid spreading. Here, we experimentally investigate gravity-driven sliding dynamics of water droplets on vertically tilted silicone layers whose viscoleasticity is characterized by the Chasset-Thirion model with the exponent m. At low Bond numbers, the sliding velocity scales with droplet size as V S $\sim$ D 2 m . While in the thin-film limit, velocity exhibits a pronounced power-law dependence on nominal substrate thickness, V S $\sim$ $Π$(h) -1 m . We rationalize these observations by quantifying viscoelastic dissipation within the soft layer and balancing it against the gravitational driving force using an energy-conservation framework. Our findings offer novel avenues for designing advanced soft coatings, anti-fouling and self-cleaning surfaces, and biomedical devices.