Silica-shell encapsulation and adhesion of VO₂nanowires to glass substrates: integrating solution-derived VO₂nanowires within thermally responsive coatings

Abstract

The binary vanadium oxide VO2 undergoes a reversible insulator—metal phase transition in response to increasing temperature accompanied by an orders of magnitude alteration of optical transmittance; the low-temperature monoclinic phase of VO2 is infrared-transmissive, whereas the high-temperature rutile phase is infrared-reflective. This remarkable property portends applications in thermally responsive spectral mirrors that can modulate infrared transmittance as a function of temperature. Using a modified Stober process, we demonstrate the constitution of conformal SiO2 shells around the VO2 nanowires. The SiO2 shells enhance the robustness of the VO2 nanowires towards thermal oxidation; the thickness of the shells is observed to depend on the reaction time. Notably, the deposition of conformal shells does not deleteriously impact the metal—insulator transitions of the VO2 nanowire cores. A modification of this approach allows for the VO2 nanowires to be embedded within a SiO2 matrix bonded to glass. The applied coatings are strongly adhered to glass as evaluated using standardized ASTM methods. The coatings exhibit promising thermochromic response and attenuate transmission of near-infrared radiation with increasing temperature.