Mechanical and Swelling Behaviors of Rubber: A Comparison of Some Molecular Models with Experiment

A review is given of several current network models (constrained chain model, localization model, liquidlike model, and eight-chain model) that have been developed to explain nonideal rubbery behavior. The stress-strain relationships for both dry and swollen networks are discussed. It is shown that the constrained chain model of Flory, Erman, and Monnerie provides the best description of the considered models for the stress-strain response of both the dry state and swollen state properties of cross-linked rubber networks. The localization model of Gaylord and Douglas fits the dry-state stress-strain data very well, but the predictions of the mechanical response in the swollen state are not as good as those obtained with the constrained chain model. The liquidlike model of DiMarzio yields reasonable description of extension behavior, but it does not explain the observed modest decrease of the elastic modulus (reduced stress) with increasing compression; nor does the liquidlike model predict the decreasing modulus with increasing swelling correctly The eight-chain model of Arruda and Boyce puts forward a stress-strain relation that includes the finite extensibility of the network chains. It is shown that at moderate deformation ratios, the eight-chain model does not provide even qualitative agreement with the experimental stress-strain data for both the dry and swollen states.