Humidity-Driven Switch in the Transparency of a Nanofiber Film for a Smart Window

Traditional smart windows use electrical signals to transform transparency. However, this electric transmission mode greatly limits their uses. Here, we have prepared a transparent PVA-co-PE/CA composite film, which can realize the reversible transformation of transparency under the stimulation of humidity. The preparation method of the composite film included simple immersion and a thermal curing process, showing high optical transparency (96.61%) and an excellent tensile strain at break of 536.34%. Once exposed to moisture stimulation, the rapid hygroscopic swelling of the composite film led to the increase in the difference in the refractive index between the citric acid filling phase and the nanofibers, which directly led to the sharp decrease in the composite film's transparency. Moreover, the composite film can be arbitrarily attached to the surface of the transparent substrate and designed as some special visualization devices or smart windows, which have a promising future in information encryption and intelligent homes.