Droplet motion driven by surface freezing or melting: a mesoscopic hydrodynamic approach.

A fluid droplet may exhibit self-propelled motion by modifying the wetting properties of the substrate. We propose a model for droplet propagation upon a terraced landscape of ordered layers formed as a result of surface freezing driven by the contact angle dependence on the terrace thickness. Simultaneous melting or freezing of the terrace edge results in a joint droplet-terrace motion. The model is tested numerically and compared to experimental observations on long-chain alkane systems in the vicinity of the surface melting point.