Dimensionally Stable Photothermally Responsive Composite Hydrogels for Thermochromic Smart Windows

Thermo‐responsive hydrogels are promising for smart windows but are often hindered by slow response kinetics and poor dimensional stability during phase transition. To address these limitations, this study synthesizes thermosensitive poly( N ‐isopropylacrylamide) (PNIPAM) microgels that are dispersed and embedded within a polyacrylamide (PAM) hydrogel matrix. Graphene oxide (GO) is incorporated to impart a rapid photothermal responsiveness to the composite hydrogel. Utilizing the photothermal conversion capability of GO, the composite hydrogel achieves an impressive response time of only 120 s under illumination at 1000 W m −2 . The composite exhibits a high solar transmittance (77.7%) at room temperature, which plummets to 1.9% above 32°C (Δ T sol = 75.8%). In a custom chamber test under 1 sun (1000 W m −2 ) illumination, the smart window stabilized the temperature at 30.4°C, which was 10.1°C lower than with standard glass, demonstrating its effective temperature regulation capability. The composite hydrogel proposed in this study shows significant potential for applications in smart window design and optical modulation due to its rapid photothermal response and superior dimensional stability.