A multiple cross-linked photo-/thermo-dual-responsive hydrogel for energy-efficient smart windows with integrated UV monitoring and information encryption

To address the limitations of conventional hydrogel-based smart windows—poor phase-transition stability, low transmittance, slow response, and limited functionality—this study developed a photo-/thermo-dual-responsive hydrogel (PNAF) via a synergistic multiple-crosslinking strategy. Composed of poly(vinyl alcohol), poly(N-isopropylacrylamide), poly(acrylic acid), and Fe 3 + ions, the hydrogel relies on cooperative hydrogen bonding and coordination interactions to form a stable network with an LCST of approximately 22.0 °C. The hydrogel exhibits high visible transmittance (∼90%), rapid thermal response (2 s), photo-response (3 min), complete blockage of 365 nm UV light at 0.09 M Fe 3+ , and a solar modulation efficiency of 68.1%. Encapsulated between glass panes, the device limits water loss to approximately 0.1% over 21 days and maintains stable optical performance over 15 heating–cooling cycles and 30 days of storage. Indoor and outdoor tests confirm effective suppression of indoor temperature rise, with an estimated cooling energy saving of approximately 7.14 W per 10 m 3 . UV irradiation reduces Fe 3+ to Fe 2+ , causing a yellow-to-colorless fading that enables visual UV dose monitoring, while localized UV writing and thermoresponsive switching allow reversible information encryption and decryption. The PNAF hydrogel thus integrates light/heat modulation, UV monitoring, photo-writing, and information security, showing broad potential for energy-efficient buildings and functional devices. Download: Download high-res image (208KB) Download: Download full-size image