Experiment of droplet anisotropic wetting behavior on micro-grooved PDMS membranes

Wetting behavior of droplets on a substrate with micro-grooves plays a key role in super-hydrophobicity. This paper aims to study the influence of groove width, droplet size, and surface tension on the anisotropic wetting behavior of droplets on micro-grooved PDMS membranes. Three types of PDMS membranes are made by mold replication. Profiles of droplets along the circumferential direction are observed by HD camera, and the 3D model of the droplet is reconstructed. Capillary forces at the three-phase contact line are obtained using the surface tension integration method. Additionally, liquid's wetting depth within the micro-grooves is calculated using an interfacial free energy equilibrium approach. The experiment shows that the micro-grooved PDMS membrane has anisotropic constrain to droplets due to wetting depth change in micro-grooves. Meta-equilibrium states at the three-phase contact line are influenced not only by substrate free energy, but also by wetting depth, interface pressure, and substrate structure.