Hydrogel Thermostat Inspired by Photoprotective Foliage Using Latent and Radiative Heat Control

Abstract

Plants such as Populus alba feature photoprotective foliage that dynamically modulates optical properties to dissipate excessive heat under high temperatures, while condensation-induced latent heating preserves warmth under cold conditions—enabling tolerance to fluctuating thermal and hydric environments. Inspired by this natural strategy, a hydrogel-based thermostat is presented that balances latent and radiative heat fluxes. The system integrates lithium ions and hydroxypropyl cellulose into a polyacrylamide matrix, providing dynamic solar reflectance, high infrared emissivity, and reversible water sorption–desorption capabilities. Thermochromic and hygroscopic responses are tunable via adjustments in hydroxypropyl cellulose and lithium ions concentrations, allowing environment-specific adaptation. Mechanical robustness is enhanced by incorporating titanium dioxide nanoparticles and applying surface treatments. Experiments and simulations demonstrate both sub-ambient cooling and above-ambient heating across diverse conditions, establishing the system as an all-season thermal regulation platform. © 2025 Elsevier B.V., All rights reserved.