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 [D iscuss. Faraday Sec. 57, 5041 (1952)]. The dynamics of the associated sprea ding is analyzed with the molecular kinetic theory. We show that the corres ponding molecular parameters vary highly nonlinearly with the relative conc entration of the heterogeneities. A model to explain this behavior is propo sed. It is predicted that small quantities of wettable heterogeneities on a nonwettable substrate will change the spreading dynamics drastically. [S10 63-651X(99)06101-2].