Hydrogel mechanics below swelling equilibrium

Abstract

Hydrogels are versatile materials due to their softness and ability to undergo large changes in water content. Their mechanics, however, are complex, being a tight coupling between fluid flow and elastic deformations. We use experiments and theory to show that this coupling simplifies when hydrogels are not fully swollen. In this regime, polymer-water affinity controls local hydration, while the much weaker polymer network elasticity plays a secondary role, setting the resulting elastic shape. This observation enables a simplified model that accurately predicts stresses and deformations.