Constitutive equations in finite elasticity of swollen elastomers

Constitutive equations are formulated for the mechanical behavior of rubber-like materials subjected to swelling under an arbitrary deformation with finite strains. Based on the Flory theory of polymer networks with constrained junctions, a novel expression is derived for free energy density of a swollen elastomer. This expression is applied to study the effect of strain rate on the elastic response of hydrogels under tension and compression.