Dependence of Wenzel–Cassie Transition on Droplet Size: The Critical Water Droplet

In this work, molecular dynamics (MD) simulations are applied to investigate the dependence of the Wenzel-Cassie transition on water droplet size. During the Wenzel-Cassie transition, the critical water droplet and corresponding critical roughness may be expected, which are respectively described as the critical radius (<i>R</i>_Droplet,c) and wetting parameter (<i>W</i>_Roughness,c). From the work, <i>R</i>_Droplet,c may be termed as the smallest droplet size at which the Cassie state is expected for the corresponding <i>W</i>_Roughness,c. In combination with the structural study of water, it is due to the structural competition between interfacial and bulk water. Additionally, <i>R</i>_Droplet,c may be dependent on the <i>W</i>_Roughness,c. It is found that the <i>R</i>_Droplet,c is influenced by the distribution and geometric characteristics of surface roughness. A denser distribution of roughness is expected to result in a lower <i>R</i>_Droplet,c. Consequently, superhydrophobicity may be influenced by the characteristics of surface roughness and the size of the water droplet. The Cassie state is achieved when the wetting parameter of roughness is less than the <i>W</i>_Roughness,c and the water droplet is larger than the <i>R</i>_Droplet,c.