The use of the van der Waals model to elucidate universal aspects of structure-property relationships in simply extended dry and swollen rubbers

Abstract

The phenomenological Mooney-Rivlin parametersC i were interpreted in terms of the van der Waals theory of networks elucidating that they are related to the effects of finite chain extensibility and cross-link fluctuations. This conclusion is empirically proven by a quantitative description of the Mooney-Rivlin parameters as derived for endlinked PDMS model networks covering a broad range of crosslinkage functionality. The empirical relationship between the van der Waals interaction parameter “a” and the average functionality then also allows a fine characterization of rubbers in use. The representation of a number of different experimental Mooney-Rivlin parameters is equivalent to having achieved a consistent characterization of networks in the range of very small strains up to largest extensions. From the description of stress-strain properties of swollen networks it is indicated that the presence of small solvent molecules, on the one hand, depresses the relative fluctuations of the crosslinks. The “deformation” due to swelling reduces, on the other hand, the maximum strain in a predictable dependence of the degree of swelling.