Superhydrophobic and thermochromic VO2-Based composite coatings for energy-saving smart windows

Architectural windows based on vanadium dioxide (VO2) that can regulate optical radiation by changing solar transmittance are of particular interest to energy conservation of buildings. Besides the critical contradiction of luminous transmittance (Tlum) and solar regulation ability (ΔTsol), as a smart window, antifouling property which also affects the optical performance is required to consider. Here, thermochromic and hydrophobic core-shell VO2 nanoparticles are prepared with tetraethyl orthosilicate and imethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride. With the adhesion effect of polydimethylsiloxane, the nanoparticles can be adhered on solid substrates. Compared with the neat VO2, the core-shell nanoparticles demonstrate increased ΔTsol (from 9.9% to 15.4%) and Tlum (from 47.9% to 51.5%), presenting a well-balanced optical property. Moreover, the presence of long alkyl chain on the core-shell nanoparticles enables high anti-wetting and self-cleaning functions. Such a composite coating has excellent wetting resistance and self-cleaning properties, enhancing the applicability as intelligent windows.