Elasticity of nematic networks and nematic effects in conventional rubbers

Abstract

Nematic rubbers are composed of cross-linked polymer chains with stiff rods either incorporated into their backbones or pendant as side chains. When nematic effects are strong, such rubbers exhbit discontinuous stress-strain relationships and spontaneous shape changes. Such a rubber is modelled using Gaussian elasticity theory, including the nematic interaction via a mean field. Results are presented for the cases of uniaxial compression and biaxial extension, and unusual phase transitions are obtained. When nematic effects are very small (i.e., T>>T c , where T c is the nematic-isotropic phase transition temperature of the rubber) it is postulated that the model is a good approximation to a conventional, nonnematic elastomer and the model is fitted to data from an isoprene rubber