HPC-PAA-PAM semi-solid hydrogel with interpenetrating network for energy-saving smart windows

Hydrogels demonstrate significant potential as materials for fabricating energy-saving smart windows. Nevertheless, their liquid nature poses challenges and renders them susceptible to leakage during operation. In this study, we developed an HPC-PAA-PAM semi-solid hydrogel through a two-step polymerization process at 80 °C, with acrylamide serving as the curing agent. The resulting hydrogel exhibited a precisely tunable lower critical solution temperature (LCST) spanning from 31.5 °C to 36.2 °C. Additionally, we constructed double-layered glass-encapsulated HPC-PAA-PAM semi-solid hydrogel smart windows, which demonstrated remarkable optical transmittance (T lum  = 88.3 %), excellent solar energy modulation (ΔT sol  = 47.9 %), and remained stability through 100 heating and cooling cycles. Thermal regulation tests conducted in model houses revealed outstanding heat-shielding performance of these hydrogel smart windows, surpassing conventional double-glazed windows and double-glass encapsulated water windows. Notably, after 90 days of outdoor exposure, the HPC-PAA-PAM semi-solid hydrogel smart window experienced only a minimal reduction in solar modulation, underlining its exceptional weather durability in practical applications. Consequently, the HPC-PAA-PAM semi-solid hydrogel presents substantial promise for the production of smart windows, particularly suited for energy-efficient buildings in tropical and subtropical regions, where it can effectively prevent the intense summer sun's heat from penetrating indoors, fostering a more pleasant indoor temperature.