Preparation and durability evaluation of vanadium dioxide intelligent thermal insulation films

Monoclinic vanadium dioxide (VO2) is a new type of thermally induced phase-transition material that undergoes a significant change in infrared transmittance during its phase transition, which makes it an excellent material for potential applications in the field of passive thermochromic smart windows. Improving the optical modulation capabilities and the durability of VO2 are crucial objectives for smart window applications. In this paper, three kinds of ethanol dispersion solutions were prepared by a nanogrinding machine using the following nanoparticles: monoclinic VO2, tungsten-doped vanadium dioxide (WVO) and silicon dioxide-coated tungsten-doped vanadium dioxide (WVO@SiO2). Polyvinyl butyral was selected as the film-forming agent, and the VO2 composite functional films were prepared by a scraping method. The ability of the prepared composite functional films to modulate light during alternating heating and cooling cycles and to resist a reduction in activity were evaluated preliminarily by an ultraviolet light irradiation method. The results show that, compared with a pure-phase VO2 film, tungsten-doped films can significantly enhance light modulation and the durability of the composite films. In addition, surface encapsulation by SiO2 in combination with introducing antioxidants also contributes to significantly improved optical properties and stability of the composite films. For example, the prepared composite films retained an infrared modulation efficiency of 49.7% at 1500 nm with a visible light transmittance of more than 60% after 65 cycles of high- and low-temperature treatments, showing excellent smart thermochromic performance, cyclic stability and promising application potential. This study is expected to provide a theoretical basis and experimental data for the preparation of stable VO2 nanomaterials and their applications to smart window films.