The thermodynamic stability of the Cassie–Baxter regime determined by the geometric parameters of hierarchical superhydrophobic surfaces

Abstract

Understanding the geometric parameters of hierarchical superhydrophobic surfaces and their impact on the thermodynamic stability of the Cassie-Baxter regime are invaluable for surface wettability–related applications. Herein, we fabricated hierarchical micro-microstructured silicone rubber surfaces having superhydrophobic properties via an industrially applicable direct replication method. The mold inserts were fabricated using photochemical milling, laser ablation, and wet chemical etching to create different hierarchical levels. We calculated surface roughness ratios and equilibrium contact angles and considered the contribution of sub-microstructures in the wettability properties via physical and statistical analyses. Comparing the calculated theoretical wettability properties and experimental measurements revealed a good agreement among all samples because of the accurate predictions of the governing wetting regime. It was worthwhile insights into the design and fabrication of superhydrophobic structured surfaces. The presence of superimposed sub-microstructures produced desirable water-repellency properties because of the reduced solid–liquid contact area as low as 0.086. Given the primary importance of the Cassie–Wenzel wetting transition on the design and fabrication of superhydrophobic surfaces, we evaluated the thermodynamic persistence of the Cassie–Baxter regime by analyzing the energy barrier to be overcome by droplets with various volumes. Finally, we discuss the contribution of the dimensional parameters of microstructures on the stability of the Cassie–Baxter regime.