Hydration Induces Dehydration: Creating Negative Swelling Gel by a Paradox

Swelling positively in water is a common behavior of hydrogels, which, however, can lead to reduced mechanical performance and stability. Enabling negative swelling represents a promising way to address those issues but is extremely challenging to realize. Here, real negative swelling hydrogels are successfully prepared for the first time through a unique molecular architecture. Specifically designed interpenetrating transformable-rigid polymer network undergoes self-assembly and collapses upon hydration, which in turn dehydrates itself. This paradoxical hydration-induced-dehydration process brings about revolutionary outcomes. Gels can now lose up to 35% weight underwater and exhibit water-strengthened mechanical properties, enhanced structural responsiveness, underwater repair ability, resistance to deformation, and swelling turn-off effect. Those unique properties allow future material development and applications to be carried out in much broader dimensions.