Influence of temperature on swelling and mechanical properties of a sulphobetaine hydrogel

The swelling and mechanical properties of a hydrogel based on the zwitterionic monomer N,N-dimethyl-N-methacryloyloxyethyl-N-(3-sulphopropyl)ammonium betaine crosslinked with ethylene glycol dimethacrylate have been determined as a function of temperature. The volumetric swelling has been found to decrease slightly with temperature. On the other hand, the Young's modulus as well as the experimental crosslink density increase with temperature. The results obtained have been explained by examining the changes with temperature of the partial molar Gibbs free energy of dilution in conjunction with the variation of its enthalpic and entropic contributions.