Peculiar Nonlinear Elasticity of Liquid Crystal Elastomers Revealed by Biaxial Stretching

Liquid crystal elastomers (LCE) are a combination of liquid crystal and elastomer. The coupling of liquid crystal alignment and rubber elasticity results in a unique mechanical property which is often called soft elasticity. The stretching in the direction normal to the initial director requires very small mechanical work due to the director rotation along the stretching axis. This is clearly observed as a finite plateau region with very low stress in the stress-strain curve. Most of the earlier characterizations of finite deformation of LCEs have been conducted using uniaxial stretching. In general, uniaxial stretching, however, provides a limited basis for comprehensive understanding of nonlinear elasticity of elastomers, because it is only a particular one among all physically accessible deformations. Present work investigates the biaxial stress-strain behavior of polydomain nematic elastomers with varying the strains independently in the two directions. We have found the peculiarity in nonlinear elasticity of LCEs which has not been characterized by uniaxial stretching measurements.