Multifunctional silica aerogel nanocoatings for enhanced thermal insulation of glass surfaces

Silica aerogels possess unique properties, such as high surface area, high porosity, low density, low thermal conductivity, and low refractive index. Their nanoscale porous structure and three-dimensional network make them promising materials for thermal insulation by effectively suppressing heat transfer via solid conduction and stagnant gas conduction. However, the presence of surface silanol groups renders conventional silica aerogels inherently hydrophilic and limits their practical applicability. In this study, transparent, thermally insulating, hydrophobic, and self-cleaning multifunctional silica-based aerogel nanocoatings were developed for glass substrates to reduce heat loss. The films were synthesized by the sol-gel method by using tetraethyl orthosilicate (TEOS) as the main silica precursor, and glycidoxypropyltrimethoxysilane (GLYMO) and aminopropyltriethoxysilane (APTES) were employed as epoxy- and amine-functional co-precursors, respectively. To further enhance the hydrophobicity, the coated surfaces were modified with trimethylchlorosilane (TMCS). The effects of surface modification and coating methods (dip and spin coating) on the optical, hydrophobic, and thermal properties were systematically investigated. The results showed that the samples produced using the spin-coated method exhibited the highest optical transparency, reaching up to 98.4%. Surface modification increased the water contact angle from 44° (bare glass) to 108°. Moreover, the fact that all surfaces exhibited contact angle hysteresis below 15° indicated effective self-cleaning capabilities. Thermal insulation performance of the coatings was evaluated comparatively using an insulated closed-box system under a constant heat source by monitoring the temperature difference between the upper and lower surfaces. Compared with all other samples, the unmodified spin-coated sample exhibited the highest temperature difference (ΔTmax = 5.38 °C) but the lowest thermal conductivity (k = 0.1231 W m⁻¹ K⁻¹). This study demonstrates that high optical transparency, effective thermal insulation, and hydrophobicity can be integrated within a single silica aerogel-based coating system. These multifunctional properties can be customized through controlled surface chemistry and coating parameters, presenting a practical and scalable strategy for energy-efficient glass applications.