Equations of state for ideal elastomeric gels

Submerged in a solvent-containing environment and subject to applied forces, a covalent polymer network absorbs the solvent and deforms, forming an elastomeric gel. The equations of state are derived under two assumptions. First, the amount of the solvent in the gel varies when the gel changes volume, but remains constant when the gel changes shape. Second, the Helmholtz free energy of the gel is separable into the contribution due to stretching the network and that due to mixing the polymer and the solvent. We demonstrate that these equations of state fit several sets of experimental data in the literature remarkably well.