Hofmeister Effect-Enhanced, Nanoparticle-Shielded, Thermally Stable Hydrogels for Anti-UV, Fast-Response, and All-Day-Modulated Smart Windows

Thermochromic smart windows offer energy-saving potential through temperature-responsive optical transmittance adjustments, yet face challenges in achieving anti-UV radiation, fast response, and high-temperature stability characteristics for long-term use. Herein, the rational design of Hofmeister effect-enhanced, nanoparticle-shielded composite hydrogels, composed of hydroxypropylmethylcellulose (HPMC), poly(N,N-dimethylacrylamide) (PDMAA), sodium sulfate, and polydopamine nanoparticles, for anti-UV, fast-response, and all-day-modulated smart windows is reported. Specifically, a three-dimensional network of PDMAA is created as the supporting skeleton, markedly enhancing the thermal stability of pristine HPMC hydrogels. Sodium sulfate induces a Hofmeister effect, lowering the lower critical solution temperature to 32 °C while accelerating phase transition rates fivefold (30 s vs. 150 s). Intriguingly, small-sized polydopamine nanoparticles simultaneously enable high luminous transmittance of 66.9% and outstanding anti-UV capability. Additionally, the smart window showcases a high solar modulation (51.2%) and maintains a 10.2 °C temperature reduction versus a glass window during all-day modulation applications. The design strategy is effective, opening up new avenues for manufacturing fast-response and durable thermochromic smart windows for energy savings and emission reduction.