Physical crosslinked hydrogel-derived smart windows: anti-freezing and fast thermal responsive performance

Thermochromic hydrogels are versatile smart materials that have many applications, including in smart windows, sensing, camouflage, etc. The previous reports of hydrogel smart windows have been based on covalent crosslinking, requiring multistep processing, and complicated preparation. Moreover, most research studies focused on enhancing the luminous transmittance (T-lum) and modulating ability (Delta T-sol), while the structural integrity and antifreezing ability, which are essential in practical applications, have been compromised and rarely investigated. Herein, we develop a new physical (noncovalent crosslinked) hydrogel-derived smart window by introducing an in situ free radical polymerization (FRP) of N-isopropylacrylamide (NIPAM) in a glycerol-water (GW) binary solvent system. The noncovalent crosslinked PNIPAM GW solutions are facilely synthesized, giving outstanding freezing tolerance (similar to-18 degrees C), a comparably high T-lum of 90%, and Delta T-sol of 60.8%, together with added advantages of fast response time (similar to 10 s) and good structural integrity before and after phase transition. This work could provide a new strategy to design and fabricate heat stimulated smart hydrogels not limited to energy saving smart windows.

Automated summary

In this study, a novel physical hydrogel-derived smart window was developed by in situ free radical polymerization of N-isopropylacrylamide (NIPAM) in a glycerol-water (GW) binary solvent system. The resulting noncovalent crosslinked PNIPAM GW solutions exhibited excellent freezing tolerance (approximately -18℃), high luminous transmittance (90%), and modulating ability (60.8% Delta T-sol), along with fast response time (approximately 10 seconds) and good structural integrity before and after phase transition.