Hydroxypropyl cellulose (HPC) hydrogel is a promising material for fabricating energy saving smart windows. However, its lower critical solution temperature (LCST = 42 degrees C) is much higher than comfortable room tem-peratures. In this work, we applied surface polymerization of acrylic acid (AA) monomers on HPC chains and synthesized HPC-polyacrylic acid (PAA) hydrogels with precisely controllable LCST in the range of 23.0-42.0 degrees C. The fabricated HPC-PAA hydrogel smart windows exhibited excellent Tlum, 22 degrees C of 91.8% and Delta Tsol, 22-40 degrees C of 73.7%, outperforming VO2 hydrogel composites and photothermal nanoparticles doped hydrogel smart win-dows. Meanwhile, cesium tungsten bronze (Cs0.32WO3) photothermal nanoparticles can be introduced to the HPC-PAA hydrogel matrix, and the near infrared (NIR) shielding ability of Cs0.32WO3 allowed significant reduction of NIR transmittance of the smart windows from 81.7% to 41.6% at 22 degrees C, and from 19.3% to 3.6% at 40 degrees C. Temperature regulation tests in model houses revealed outstanding heat-shielding performance of Cs0.32WO3 (0.4 wt%)/HPC-PAA hydrogel smart windows, especially compared with ordinary double-glass win-dows. Furthermore, the HPC-PAA hydrogel and Cs0.32WO3 (0.4 wt%)/HPC-PAA hydrogel are non-toxic, biocompatible, low-cost, suggesting their suitability for energy-saving smart window applications.
