Droplet spreading on heterogeneous substrates using molecular dynamics

Using molecular dynamics, it is shown that the equilibrium contact angle of a sessile drop placed on a heterogeneous substrate follows Cassie's law [Discuss. Faraday Soc. 57, 5041 (1952)]. The dynamics of the associated spreading is analyzed with the molecular kinetic theory. We show that the corresponding molecular parameters vary highly nonlinearly with the relative concentration of the heterogeneities. A model to explain this behavior is proposed. It is predicted that small quantities of wettable heterogeneities on a nonwettable substrate will change the spreading dynamics drastically.