(265d) Swelling of Crosslinked Elastomers: Frenkel, Flory, Rehner Revisited

The swelling and mechanical properties of networks are intimately tied together through the free energy function as it is affected either by chain stretching (elastic free energy) or through the mixing of the polymer with the solvent (usually through a Flory-Huggins estimate).  Frenkel, then Flory and Rehner (FFR) developed a simple way of looking at this problem by simply balancing the elastic and mixing contributions to the chemical potential at swelling equilibrium.  Much work has been done to examine this model, often in a way that suggests that something is missing or that the model itself is incorrect.  In this presentation we examine the FFR model and show that it is correct for polymer networks swollen in organic liquids.  We demonstrate that anomalous peaks in the swelling activity parameter S (or dilational modulus) are artifacts of experimental methods and we further show that, once the peak in S is removed, quantitative agreement is obtained between mixing and elastic contributions to the free energy with the simple addition of a cross-link dependent interaction parameter.