Concurrent stiffening and softening in hydrogels under dehydration

Hydrogels are an extraordinary soft matter system that serve as a laboratory for a rich plethora of multiphysical phenomena and find applications that range from biocompatible sensors to soft robots. Here, we report a peculiar experimental observation suggesting concurrent stiffening and softening in hydrogels during the dehydration process. Theories based on Flory's work fail to capture the scaling of mechanical behavior with water content, observed in our experiments. We perform coarse-grained molecular dynamics simulations to elucidate the mechanisms underpinning the odd softening-stiffening behavior during dehydration and propose a theoretical model to correctly represent the underlying physics and the divergence from Flory-based theories.