Abstract
Interaction of water on heterogeneous nonwetting interfaces has fascinated researchers' attention for wider applications. Herein, we report the evolution of hierarchical micro-/nanostructures on superhydrophobic pseudoboehmite surfaces created from amorphous Al2O3 films and unraveled their 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 Al2O3 film have been extensively analyzed, which helped in attaining the optimal Cassie-Baxter state. The evolution of pseudoboehmite films has been structurally characterized using grazing incidence X-ray diffraction, field-emission scanning electron microscopy, high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and atomic force microscopy. Interfacial surface energy components on the structured superhydrophobic surface exhibited a very low surface energy of ∼4.6 mN/m at room temperature and ultrahigh water contact angle >175°. The interaction between water droplets on the nonwetting surface was comprehended and correlated to the temperature-dependent surface energy properties. The surface energy and wettability of the structured pseudoboehmite superhydrophobic surface exhibited an inverse behavior as a function of temperature. Interestingly, the superhydrophobic surface exhibited "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. These high-temperature wetting transition studies could be potentially valuable for solid-liquid systems working at nonambient temperatures, and also this approach can pave new pathways for better understanding of the solid/liquid interfacial interactions on nanoengineered superhydrophobic surfaces.
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