Evolution of Temperature-Driven Interfacial Wettability and Surface Energy Properties on Hierarchically-Structured Porous Superhydrophobic pseudo-Boehmite Thin Films

Interaction of water on heterogeneous non-wetting interfaces has fascinated researchers' attention for wider applications. Herein, we report the evolution of hierarchical micro/nanostructures on superhydrophobic pseudo-boehmite surfaces created from amorphous Al O films and unraveled its temperature-driven wettability and surface energy properties. The influence of hot water immersion temperature on the dissolution-reprecipitation mechanism and the surface geometry of the Al O film have been extensively analyzed, which helped in attaining optimal Cassie-Baxter state. The evolution of pseudo-boehmite films have been structurally characterized using Grazing Incident X-Ray Diffraction (GIXRD), Field-Emission Scanning Electron Microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS) and Atomic Force Microscopy (AFM). Interfacial surface energy components on structured superhydrophobic surface exhibited very low surface energy of ~4.6 mN/m at room temperature and exhibited ultra-high water contact angle >175 . The interaction between water droplets on the non-wetting surface was comprehended and correlated to the temperature-dependent surface energy properties. The surface energy and wettability of the structured pseudo-boehmite superhydrophobic surface exhibited an inverse behavior as a function of temperature. Interestingly, the superhydrophobic surface exhibited the 'Leidenfrost effect' below the boiling point of water (67 C) which is further correlated with the intermolecular forces, interfacial water molecules and surface terminated groups. This high-temperature wetting transition studies could be potentially valuable for solid-liquid systems working at non-ambient temperatures and also this approach can pave new pathways for better understanding of the solid/liquid interfacial interactions on nano-engineered superhydrophobic surfaces.