Swelling and elasticity of poly (N-isopropylacrylamide-co-4-vinyl benzene sulfonic acid sodium salt) hydrogels

The mechanical properties and the swelling behavior of hydrogels based on N-isopropylacrylamide (NIPA) and 4-vinylbenzenesulfonic acid sodium salt (styrene sulfonate, SSA) monomers were investigated. The mole fraction of SSA in the comonomer feed varied between 0 and 1, whereas the crosslinker ratio was fixed at 1/85. Both the swelling and the elasticity data of the hydrogels swollen in water show that they are in the non-Gaussian regime. The exponents found for the charge density dependence of the equilibrium swelling ratio as well as for the volume dependence of the gel elastic modulus are in good agreement with the predicted course of the non-Gaussian elasticity of swollen hydrogels. (C)2004 Wiley Periodicals, Inc.