Unusual Temperature Dependence of Water Sorption in Semicrystalline Hydrogels

Water vapor sorption is a ubiquitous phenomenon in nature and plays an important role in various applications, including humidity regulation, energy storage, thermal management, and water harvesting. In particular, capturing moisture at elevated temperatures is highly desirable to prevent dehydration and to enlarge the tunability of water uptake. However, owing to the thermodynamic limit of conventional materials, sorbents inevitably tend to capture less water vapor at higher temperatures, impeding their broad applications. Here, an inverse temperature dependence of water sorption in poly(ethylene glycol) (PEG) hydrogels, where their water uptake can be doubled with increasing temperature from 25 to 50 degrees C, is reported. With mechanistic modeling of water-polymer interactions, this unusual water sorption is attributed to the first-order phase transformation of PEG structures, and the key parameters for a more generalized strategy in materials development are identified. This work elucidates a new regime of water sorption with an unusual temperature dependence, enabling a promising engineering space for harnessing moisture and heat.

Automated summary

Water vapor sorption plays a crucial role in various applications, but conventional materials tend to capture less water vapor at higher temperatures. However, a recent study reports an inverse temperature dependence of water sorption in poly(ethylene glycol) (PEG) hydrogels, where the water uptake can be doubled with increasing temperature from 25 to 50 degrees C. This unusual phenomenon is attributed to the first-order phase transformation of PEG structures, providing insights for developing new materials for moisture and heat harnessing.