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

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.

Double-Sided, Omnidirectional γ-AlOOH Hierarchical Nanostructures: Imparting Enhanced Antireflective Properties with Self-Cleaning Capacity for Optical Devices

“…The detailed growth mechanism of the alumina film subjected to HWI temperature has been thoroughly discussed in our previous report. 22 The variation in transmittance for four different thicknesses obtained at different HWI temperatures is shown in Figure 3j. The transmittances of the glass substrate with (a) no AR coating (uncoated glass), (b) single-side-coated AR glass, and (c) double-side-coated AR glass are shown in Figure S4, Supporting Information.…”

“…In our previous reports, the growth mechanism involved in the formation of a hierarchically structured γ-AlOOH surface has been proposed by careful structural and morphological evaluation and subsequently a method for large-scale production of self-cleaning coatings for solar panels has been reported. , However, in addition to superhydrophobicity, optical transparency and durability of self-cleaning coatings are highly essential for deploying them for solar panel applications. In this scenario, for the first time, a novel method to fabricate double-sided γ-AlOOH photonic nanostructures with graded RI created on glass using dip-coating, which possess omnidirectional AR properties along with self-cleaning capability, has been demonstrated in the present investigation.…”

Spontaneous dewetting transitions of droplets during icing & melting cycle

“…Two kinds of surfaces are fabricated: the surfaces with different microcones heights and constant pitch and the surfaces with different microcones pitches and constant height (Supplementary Figs. [20][21][22] and Supplementary Method 2). In the figure, microcones pitch is fixed at 35 μm while microcones heights vary from 35 μm to 55 μm.…”

“…Generally, one of the CB state and the Wenzel state is metastable, and a large energy barrier exists to make the spontaneous transition to the other impossible [18][19][20][21][22][23][24][25] . To achieve the W2C transition, many researchers have adopted various methods, such as magnetic forces 18 , high-temperature driving forces [19][20][21] , ultrahigh slenderness ratio 22,23 , and mechanical vibrations 24,25 . However, these external assistances are enormously challenging to apply in practice due to the constraints of actual working conditions and unsatisfied continuous energy input.…”

“…By adjusting laser processing parameters (Supplementary Table2), we achieve precisely tunable heights and pitches of the micro-nanostructure on the MCNP surfaces. Two kinds of surfaces are fabricated: the surfaces with different microcones heights and constant pitch and the surfaces with different microcones pitches and constant height (Supplementary Figs [20][21][22]. and Supplementary Method 2).…”