A novel bidirectional fast self-responsive PVA-PNIPAM/LimCsnWO3 composite hydrogel for smart window applications

The photo-thermochromic materials with self-regulation of solar light transmittance have attracted a increasing attention because of its potential in smart windows and energy-saving field. Here, a novel bidirectional fast self-responsive PVA-PNIPAM/LimCsnWO3 composite hydrogel has been fabricated by coupling the high near-infrared (NIR) shielding/photothermal effect of LimCsnWO3 particles and thermally light-adjusting properties of polyvinyl alcohol-poly(N-isopropylacrylamide) (PVA-PNIPAM) hydrogels. Under solar irradiation, the photothermal effect of LimCsnWO3 particles can drive the phase transition of PVA-PNIPAM hydrogel, thus the composite hydrogel exhibits bidirectional fast self-responsive spectral transmission/shielding switching function. When the LimCsnWO3 (LCWO) particles doping amount is 1.67 × 10−3 g/mL, the maximum NIR shielding rate of the sandwich structured smart window filled with the composite hydrogel can reach up to 99.77%, meanwhile the smart window can allow part of the visible light to enter the room for day lighting, with the visible light transmittance before and after its optical switching being 67.48% and 16.76%, respectively, and the simulated thermal insulation test results indicate that the thermal insulation temperature difference between external surface of the smart window and indoor air is 30 °C higher than that of ordinary hollow glass windows. Moreover, due to the high photothermal effect/NIR shielding of LimCsnWO3 and specific heat capacity of PVA-PNIPAM hydrogel, the obtained smart window exhibits strong thermal insulation and heat storage capabilities. The photothermal solar transmittance self-regulation mechanism of the PVA-PNIPAM/LimCsnWO3 composite hydrogel has been discussed. This research has a great significance for the development of high energy efficient smart windows.