Molecular dynamics simulations of wetting behaviors of droplets on surfaces with different rough structures

Aiming at the wall-wetting problem in internal combustion engines, to actively control the behaviors of fuel droplets after hitting the walls, the molecular dynamics method is used to investigate the effects of the surface wettability and rough structure on the static and dynamic wetting behaviors of the droplets. The results show that the droplet diameter has little influence on the intrinsic contact angle. With the decrease of the solid-liquid interaction coefficient, the interaction between the wall and the droplet is weakened, and the wetting state changes from the Wenzel state to the Cassie state, resulting in an increase in the static contact angle. As the ratio of the solid-liquid contact area to the composite contact area decreases, it is easier for the droplet to reach the Cassie state. Compared with the smooth surfaces, the structures of the rough surfaces have an inhibitory effect on the spreading of the droplets. The apparent contact angles of the droplets on the rough surfaces with different structures are larger than their intrinsic contact angles on the smooth surfaces. The secondary boss-shaped structures can significantly enhance the surface oleophobicity. In addition, with the decrease of the solidliquid interaction coefficient, the contact angle hysteresis reduces. Compared with the Wenzel state, the droplet in the Cassie state has a smaller contact area with the surface, which makes the interaction between the wall and the droplet weaker, leading to a decrease in the contact angle hysteresis.