Understanding droplet collision with superhydrophobic-hydrophobic–hydrophilic hybrid surfaces

Abstract

This study uses a two-phase finite volume method to investigate the dynamics of Newtonian and non-Newtonian droplets impacting onto hybrid surfaces with various wettabilities. Six configurations with different substrate contact angles are tested ranging from hydrophilic, hydrophobic, and superhydrophilic as well as a combination of them. The temperature-dependent properties are applied to model the Newtonian droplets, and the Arrhenius law which is a relation between viscosity and shear rate is incorporated for the non-Newtonian rheology. The results show that for a hybrid surface with linear wettabilities varying from hydrophilic to hydrophobic to superhydrophobic, the maximum spreading factor is larger for both Newtonian and non-Newtonian droplets in comparison to any other surface configurations considered in this study. However, this spreading factor is minimum when a stepwise superhydrophobic-hydrophobic-hydrophilic hybrid surface is examined. Further, the residence time of Newtonian droplet has the maximum value when collides upon a hybrid surface with linear wettability distribution ranging from hydrophilic to superhydrophobic. However, the maximum value of residence time for the non-Newtonian droplet is achieved when the stepwise pattern of hydrophilic to superhydrophobic is adopted.