Investigation of wetting states and wetting transition of droplets on the microstructured surface using the lattice Boltzmann model

Abstract

In this study, the wetting states and wetting transition of droplets on the microstructured surfaces are investigated using the multiphase lattice Boltzmann method. The Cassie-Baxter (Cassie) and Wenzel wetting states on the rough surfaces are captured through the simulations, and the stability of Cassie state and the wetting transition are then studied and discussed by simulating the evaporation of droplets on several specified microstructured surfaces. The simulated apparent contact angles of the droplet on various rough surfaces fit the theoretical predictions very well. The results also present the coexistence of the Wenzel and Cassie states when the substrate is moderately hydrophobic with its Young’s angle smaller than the critical angle. In addition, the “De-pinning” wetting transition from Cassie to Wenzel state is observed for the moderately hydrophobic substrate once the droplet reduces to its critical radius, while the stable Cassie state is obtained when the substrate’s Young’s angle larger than the critical angle. The simulated critical radii for wetting transition are in quantitative agreements with the analytical values for different surface geometries and Young’s angles. This work provides mesoscopic information necessary for understanding the wetting phenomena on microstructured rough surfaces.