Evaluation of the solid-liquid contact area fraction of drops deposited on rough surfaces beyond the Wenzel regime

In this work, we studied the wettability of hydrophobic surfaces fabricated with three different materials (PTFE, PDMS and paraffin wax) over a wide range of roughness. We estimated the Advancing, Receding and Most-Stable contact angles and we identified the transition from a homogeneous wetting regime (Wenzel) to a hybrid wetting regime (Cassie-Baxter). Using a modified Cassie-Baxter equation which considers the chemical heterogeneity of the samples, we were able to determine the solid area fraction within the contact area. This way, we designed a methodology to identify the superhydrophobic degree of rough-hydrophobic surfaces.