Hydrogel-elastomer hybrid integrated with radiative and evaporative cooling for passive temperature-adaptive regulation

Abstract

Passive temperature regulation with spectrum modulation and evaporative cooling in a zero-energy consumption manner has gained rapid prominence, proposing an available strategy for the environmental crisis. However, dynamic temperature regulation responding to environmental stimuli remains a formidable challenge. Herein, thermochromic hydrogel-elastomer hybrids were constructed using polyacrylamide (PAM) hydrogel, PVA-Borax-Poly(N-isopropylacrylamide) (PBN) hydrogel and boric acid-polydimethylsiloxane (B-PDMS) elastomer. Boronate ester bonds that were generated between the diol and the hydroxyl groups allowed the self-healing of PBN hydrogels and B-PDMS elastomers, which facilitated the fabrication of PBN/B-PDMS hybrid. Moreover, PBN_0.5 hydrogel achieved a reversible transparent-opaque turn when the temperature across 32.09 °C, which brought a transmittance modulation of 85.18 % as well as reflectance modulation of 42.48 % in the solar spectrum, respectively. Moreover, the infrared emissivity of PAM hydrogel, PBN hydrogels and B-PDMS elastomer was maintained at a high level. The hybrid made the temperature approximately 1 °C lower than the ambient temperature under the solar irradiance of 700 W m⁻² and a temperature gap of 4.21 °C was obtained in an outdoor test. The hybrid coverage reduced the temperature of the banana surface and avoided sunlight-induced damage to the bananas, offering a sustainable approach to food quality preservation.