PAM-PNIPAM/W-doped VO2 thermochromic hydrogel film with high solar modulation capability for smart windows deployment

Passively responsive thermochromic smart window, which can modulate indoor incident solar light automatically at relatively high outdoor temperature, is a practical energy-saving device for construction and automotive industries. In this paper, a thermochromic composite hydrogel film based on W-doped vanadium dioxide (W-VO2), poly N-isopropyl acrylamide (PNIPAM) and polyacrylamide (PAM) is presented and this hydrogel film was prepared between two quartz substrates to form the sandwich structured smart window. In this thermochromic system, 2 wt% monoclinic W-VO2 were dispersed in the hydrogel film with the thickness of 0.1 mm. The introduction of PAM changes the flow-state PNIPAM microgel to hydrogel, which dramatically improved the practicality of the PNIPAM-based smart window. When the outdoor temperature is higher than 40 °C, the solar modulation capacity of this passive smart window, with a high luminous transmittance of 72% at 25 °C, can reach 46.3%. The smart window possesses high solar modulation ability and more than 20% luminous transmittance even after 40 times high temperature durability tests.