research


tough hydrogels
subzero temperatures
non-freezing ionic devices
ice-salt slurry phase
freezing point depression


Xavier P. Morelle, Widusha R. Illeperuma, Kevin Tian, Ruobing Bai, Zhigang Suo, Joost J. Vlassak
https://onlinelibrary.wiley.com/doi/...adma.201801541

Abstract:*
Hydrogels consist of hydrophilic polymer networks dispersed in water. Many applications of hydrogels rely on their unique combination of solid-like mechanical behavior and water-like transport properties. If the temperature is lowered below 0°C, however, hydrogels freeze and become rigid, brittle, and non-conductive. Here, we demonstrate a general class of hydrogels that do not freeze at temperatures far below 0°C, while retaining high stretchability and fracture toughness. These hydrogels are synthetized by adding a suitable amount of an ionic compound to the hydrogel. The present study focuses on tough polyacrylamide-alginate double network hydrogels equilibrated with aqueous solutions of calcium chloride. The resulting hydrogels cab be cooled to temperatures as low as -57°C without freezing. In this temperature range, the hydrogels can still be stretched more than four times their initial length adn have a fracture toughness of 5000 J m-2. It is anticipated that this new class of hydrogels will prove useful in developing new applications operating under a broad range of environmental and atmospheric conditions.








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