Thermochromic hydrogels for synergistic mechano-optical properties and global energy saving potential

As building energy consumption and carbon emissions continue to rise, minimizing energy loss through windows-major heat exchange pathways-has become an urgent challenge. To reduce building energy consumption by improving windows' thermal insulation and light modulation, this study develops a thermoresponsive hydrogel named PDH, based on a poly(N-isopropylacrylamide) backbone, for use as a window coating. The hydrogel exhibits considerable visible light transmittance (97.92%) and high solar modulation ability (81.70%), along with favorable mechanical properties, which enable its stable and direct application onto single-pane glass surface, thereby simplifying the conventional glass-hydrogel-glass structure in smart windows. In practical building applications, PDH hydrogel shows significant thermal regulation, with an average daytime indoor temperature reduction of 6.95 °C and energy savings of 384.04 kJ m^-2. Furthermore, a global energy-saving and carbon-reduction model is developed using climate data to support the assessments and applications of PDH hydrogels across various climate regions.