The elasticity of nematic networks

Abstract

AbstractNematic rubbers are composed of crosslinked polymer chains with stiff rods either incorporated into their backbones or pendant as side chains. When nematic effects axe strong, such rubbers exhibit discontinuous stress‐strain relationships and spontaneous shape changes. We model such a rubber using Gaussian elasticity theory, including the nematic interaction via a mean field. Results are presented for the cases of uniaxial extension and compression. Under uniaxial extension the rubber can undergo a first order phase transition to a uniaxial nematic phase. Under uniaxial compression first or second order transitions are possible to genuinely biaxial nematic states with biaxial strains. When nematic effects are very small (i.e. T >> Tc where Tc is the nematic‐isotropic phase transition temperature of the rubber) we postulate that the model is a good approximation to a conventional, non‐nematic elastomer, and fit our model to data from an isoprene rubber.