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

Abstract 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.