Temperature-Responsive Double-Network Cooling Hydrogels

Skin inflammation can occur due to the immune response of the body, infections, and injuries and lead to an increase of skin temperature. Cooling inflamed skin can relieve pain and efficiently dissipate heat. Evaporative cooling hydrogels are hence promising materials for preparing flexible dressings for cooling inflamed skin because of the high latent heat of water vaporization (∼2450 J·g–1 at 100 °C and 1 atm). We fabricate here a double-network hydrogel formed with poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAMPS) and poly(N-isopropylacrylamide) (PNIPAM). Water can be released by the PNIPAM network above ∼32 °C, which is close to human’s skin temperature, and provides heat dissipation and cooling through evaporation. The network formed with PAMPS delays the release of water from the hydrogels. Large and prolonged cooling performance of a skin model and enhanced mechanical properties are obtained with the proposed design. Compared to other reported hydrogels for passive cooling, our material demonstrates a superior cooling power with lower temperature. This design of the hydrogel can be adapted for cooling other structures such as photovoltaic panels or roofs of buildings.