Wetting state transition of a liquid gallium drop at the nanoscale.

Wetting state transition regulated by surface roughness has increasing importance for its wide applications. Molecular dynamics simulations have been performed to study the wetting state transition induced by surface roughness in the gallium-carbon system. There is a transition from the Wenzel state to the Cassie state when the roughness is changed. When the surface roughness is more than 1.8, the gallium droplet is in a Cassie state, but when it is less than 1.6, it is in the Wenzel state. The substrate composed of irregular pillars has a similar effect on the wetting state transition. Besides, distinctive variations occur in the interface tension, the mean-squared displacement, the wetted surface and the interaction energy as the wetting state changes, which are further explained by the proposed model. This study would provide significant guidance for designing superhydrophobic surfaces in the future.