Influence of Trapezoidal Cavity on the Wettability of Hydrophobic Surface: A Molecular Dynamics Study

In this study, the behaviors of water droplets on hydrophobic surfaces with different cavities are studied by molecular dynamics. Hydrophobic surfaces with different cavities are designed and simulated: trapezoidal cavity with the same lower width, upside down trapezoidal cavity with the same lower width, and so on. The results show that the influence of the upper width and the depth of the cavity on the contact state and contact angle is different for different trapezoidal cavities. For example, for the trapezoidal cavity with the same lower width, the upper width decreases with the increase of the cavity depth. In such a scenario, the upper width and depth of the cavity collectively promote the droplet transition into the Cassie state from the Wenzel state, but the effect of the upper width and depth on the contact angle is opposite, and the decrease of the upper width of the cavity is the dominant factor, which leads to a decrease in the contact angle. Then, we have built trapezoidal cavities with different base angles. The influence of different base angles on wettability is also discussed, and it is found that an increase in base angle can significantly delay the transition from Cassie state into the Wenzel state.