Broadband Thermal Management Using Smart Cooling Films

With the escalating trend of climate change, we are under severe pressure to increase the resilience of commercial and residential buildings and vehicles. Smart lighting and thermal management of windows promise to improve indoor thermal comfort with minimum added carbon footprints. We report a passive smart cooling technology for thermal management throughout the spectrum from visible to mid-infrared regions by using a thermochromic hydrogel network integrated with an optically transparent polymer coating for radiative cooling. We have achieved excellent optical properties, including luminous transmittance of 81.8% and solar transmittance modulation of 74.8%, to intelligently minimize direct solar radiation. Notably, merging the light management of thermochromic hydrogel networks with the thermal management of daytime radiative cooling films enables us to minimize secondary radiation from hot window surfaces, contributing to overall cooling power. To the best of our knowledge, this is the first demonstration of the integration of a thermochromic smart medium and passive radiative cooling film into a single cooling apparatus in a field test. Through this integration, we achieved an indoor temperature drop of up to 5.1°C on summer days with zero energy consumption.<br/>Additionally, our material and device designs offer advances far beyond spectrum tunability and cooling power. The mechanical flexibility and moldability of the hydrogel network promise extensive applications for our technology in buildings, vehicles, and other complex geometric shapes with intelligent cooling needs, distinguishing it from any prior liquid-based counterparts. We believe that the broad thermal management of thermo-responsive hydrogel networks and visually transparent radiative cooling coatings could usher in a new paradigm for extending the scope of space temperature control, bringing tangible benefits to real-world applications aimed at alleviating global cooling needs.