Excluded volume effects on stress transmission in rubber elasticity

Abstract

The generally accepted view of the nature of excluded volume effects in rubber elasticity is that they serve only to provide an isotropic pressure which maintains the system at constant volume. This question is reexamined here by the computer simulation of an idealized model representing one chain of a network enclosed in a tube which provides the confining effect of the remaining chains. This model demonstrates that intramolecular excluded volume effects make a substantial contribution to the stress transmitted across an arbitrary interior plane of the system. Furthermore, the magnitude of this contribution depends upon the chain extension. It is therefore conjectured that intramolecular excluded volume effects may make an anisotropic contribution to the stress tensor in rubber elasticity. The model results also cast light on the possibility of a statistical mechanical formulation for rubber elasticity in which only the atoms of an interior portion of the network are treated explicitly, while the surrounding network serves as heat bath and loading device.