Hydrophobic zinc-tellurite glass system as self-cleaning vehicle: Interplay amid SiO2 and TeO2

Abstract

Cost-effective, environmental amiable and maintenance free glasses with improved hydrophobic activity are needed for diverse industrial applications. Pollutant and dirt depositions on glasses that cause the visual obscurity and damages of the cultural heritages require inhibition. The underlying mechanism of hydrophobic interactions assisted self-cleaning traits of glass is poorly understood. It has been shown that excellent hydrophobic glass with water contact angle (WCA) above 90^o and very low surface wettability can be achieved by controlling the surface roughness (SR), where liquid droplets remain perfectly spherical on such surfaces (literally without touching) before being self-cleaned (rolls off). Moreover, selection and optimization of constituent materials composition as well as the preparation technique play a significant role towards such success. Most of the previous attempts for the self-cleaning glass preparation were made via coating strategy on glass surface. Yet, preparation of super-hydrophobic glass surfaces with self-cleaning attributes remains an open challenge. Driven by this idea, we prepared a new glass system of composition (80 x) TeO₂-20ZnO-(x)SiO₂ (x = 0, 0.03, 0.06, 0.09 and 0.12 mol%) by melt-quenching method, where the proportions of SiO₂ and TeO₂ were interplayed. As-prepared samples (thin pellet without coating) were characterized using atomic force microscopy (AFM) and video contact angle (VCA) measurements. The effects of SiO₂ concentration on the glass SR, surface energy and hydrophobic properties were evaluated. Glass 0.06 mol% of SiO₂ revealed the optimal WCA of 112.39º and SR of 7.806 nm. It was established that a trade-off between SiO₂ and TeO₂ contents in the studied glasses could produce super-hydrophobic surface (WCA over 90º), leading to great opportunities for diverse self-cleaning applications.