Enhanced Atmospheric Water Uptake of Hydrogels at Elevated Temperatures

To prevent the dehydration of living organisms, it is crucial to obtain and retain water, especially in hot weather. However, most materials, including plants, biological tissues, and inorganic sorbents, can lose more water at a high temperature and capture more water at a low temperature, because of the exothermic water vapor adsorption. Here, we discover a class of hydrogels that exhibit enhanced atmospheric water uptake when the temperature is elevated. For example, the adsorbed water in hydrogels is doubled when we increase the temperature from 25°C to 75°C and maintain 20% relative humidity. This abnormous temperature dependence of water vapor adsorption can be attributed to the first-order phase transition of polymer networks. We also developed a thermodynamic theory to analyze and predict the equilibrium water vapor adsorption at different temperatures and relative humidity. Our finding has profound implications for thermal energy management and atmospheric water harvesting.