PNIPAm/HPC/NaCl/CWO Composite Hydrogel with Tunable Phase Transition and Broadband NIR Shielding for Smart Window Applications.

Thermochromic hydrogels have attracted considerable attention for applications in energy-saving smart window owing to their dynamic solar transmittance modulation capability. However, achieving a combination of high mechanical strength, superior optical performance, efficient near-infrared (NIR) shielding, and photothermal conversion within a single hydrogel system remains a significant challenge. Herein, a multifunctional thermoresponsive hydrogel-based smart window (NHNC) was constructed via a simple one-pot strategy. In this system, poly(N-isopropylacrylamide) served as the thermoresponsive matrix, hydroxypropyl cellulose was employed to enhance mechanical properties and regulate the phase-transition behavior through modulation of the hydrogen-bonding network, and NaCl was introduced to precisely tune the lower critical solution temperature (LCST) via the salting-out effect. Notably, CsxWO3 nanoparticles endowed the composite hydrogel with efficient broadband NIR shielding through free-carrier absorption and localized surface plasmon resonance. Owing to the synergistic regulation of these components, the as-prepared NHNC hydrogel exhibited a tunable LCST of ∼28.7 °C, high visible-light transmittance (>98%), and favorable solar modulation ability (∆Tsol = 68.12%). Meanwhile, the system maintained excellent antifreezing performance at low-temperature (-17 °C) and exhibited enhanced mechanical strength. The incorporation of CsxWO3 also endowed superior UV/NIR shielding capability. In addition, the composite hydrogel exhibited excellent thermal regulation performance and long-term operational stability. It enabled great promise for building energy savings, thermal comfort control, and visual privacy management, while also demonstrating climatic adaptability.