Effect of Swelling and Deswelling on Mechanical Properties of Polymer Gels

Polymer gels exhibit some unique features that are not seen in the uncrosslinked polymer system, rubber elasticity and swelling. In this paper, we review our recent studies towards the molecular understanding of the relationship between the elasticity and the swelling ratio using the Tetra-PEG gels. The dependence of the polymer volume fraction of interest state (phi(m)) on the elasticity exhibits the power-law behaviors and the crossovers at phi* and phi(c) due to the presence of the excluded volume effect and the supercoiling. The Obukhov model successfully describes the power-law behaviors. The fractal dimension of network strands (D-f) based on the stress-elongation relationships using the Pincus blob revealed that the gyration radius of the network strands decreases with deswelling in affine manner. As for the equilibrium swelling, the definite phi(0)-dependences of phi(m) and E-s are observed due to the effect of the excluded volume effect at preparation state. The Obukhov model can predict this result, while the C* theorem cannot predict it. Using the polymer gels with precisely controlled network structures, we successfully verify the molecular models to describe the relationships between the elasticity and the swelling degree of polymer gels.