Supramolecular Hydrogels Inhibit Water Crystallization at Cryogenic Temperature

Ice crystallization with its large volume expansion of water is a destructive force that can reshape geological formations, cause costly structural damage, and limit the ability to cryogenically preserve biological media such as blood and organs. Controlling ice nucleation and growth is of great technological importance where additives including salts and aqueous polymers have been shown to delay nucleation and limit the crystallization rate, but their overall efficacy is limited. Inspired by the two methods by which nature manipulates the formation of ice (hydrogen bonding macromolecules and nanoconfinement between hydrophobic moieties), we report a family of supramolecular hydrogels with tunable supercooling capabilities. Through modulation of both interactions of the water with the hydrophilic base of the hydrogel and spacing of hydrophobic crosslinks, >99.0 wt% of the water in the hydrogel can be supercooled to 128 K and resist further crystallization on re-heating towards the melting point. A combination of SAXS and SANS is used to understand how these hydrogels evolve on cooling, while the water structure is probed with WAXS. This ability to inhibit ice formation in soft matter is unprecedented and provides new concepts in the quest to control water crystallization.