Temperature-Responsive On-Off Control over Water Evaporation Achieved via Sweat-Gland-Mimetic Composites

Responsive cooling materials that mimic sweat glands have gained popularity because they are efficient and do not require artificial energy sources. Temperature-responsive hydrogels sweat above their volume transition temperature through the release of water and exhibit excellent cooling ability. However, thus far, practical applications have not been possible because the water in these materials cannot be preserved in cool environments. To address this issue, this paper presents a simple composite of poly(N-isopropylacrylamide) and polydimethylsiloxane that offers excellent on-off control over water evaporation and can be used repeatedly; the proposed composite features an evaporation rate of 2.97 g/h above the lower critical solution temperature (LCST) and 0.08 g/h below the LCST. This 35.7-fold change in the water evaporation rate is comparable to that in mammalian sweat glands. The responsive on-off control relies on the structures of the composite and the dry layers formed on the surface of the composite in cool environments. The proposed material effectively regulates water evaporation and offers a novel, low-cost cooling strategy suitable for numerous applications.