A photo-/thermo-dual-responsible CsxWO3/PNIPAM composite hydrogel for energy-efficient windows

Cesium tungsten bronze (CsxWO3) is an important functional material for energy efficient windows, showing excellent near infrared (NIR) shielding ability but no optical switching ability. In this paper, we demonstrate a photo-/thermo-dual-responsible CsxWO3/PNIPAM composite by dispersing CsxWO3 nanoparticles into PNIPAM hydrogels. Combination of the photothermic conversion ability of CsxWO3 with the thermochromic property of PNIPAM makes this hydrogel responds to both thermo- and photo-stimuli. In sunlight, the CsxWO3 component converts the absorbed infrared light into heat, triggering the phase transition of PNIPAM and switching the hydrogel into visibly opaque state (for example, transmittance decreased from 58% down to 15% at 590 nm). At the same time, an ambient temperature >32 °C can also initiate the phase transition of PNIPAM. Therefore, a photo- and/or thermo-derived transition between a 'transparent NIR-shielding' state and a 'full-solar-spectrum shielding' state is achieved, making it highly attractive for the applications as energy efficient windows for buildings in hot climate.