Semisoft elasticity and director reorientation in stretched sheets of nematic elastomers

Abstract

A two-dimensional effective model for the semisoft elastic behavior of nematic elastomers is derived in the thin film limit. The model is used to investigate numerically the force-stretch curves and the deformed shape, and to resolve the local patterns in the director orientation in a stretching experiment. From the force-stretch curves we recover the two critical stretches which mark the transition from hard to soft and back to hard response. We present an analytical model for their dependence on the aspect ratio of the sample, and compare it with numerical results.

Orientational order and finite strain in nematic elastomers

“…As support for soft deformations and the neo-classical model, Verwey, Warner & Terentjev 21 interpreted the observed formation of stripes as a consequence of soft elasticity, which has been further investigated by DeSimone & Dolzmann 22 and Conti et al 23,24 . The recent experiments of Martinoty et al 25 , however, appear to contradict the assumptions of soft elasticity.…”

“…DeSimone & Dolzmann 22 and Conti et al 23,24 considered nematic elastomers subject to the constraint detA = detA * . Essentially, this normalization imposes the requirement that the volume occupied by a generic polymer chain remains unchanged regardless of shape changes and, thus, embodies what might be considered a constraint of microstructural incompressibility.…”

“…In so doing, we consider two models. The most basic of these has been used in studies on the effect of deformation on the striping instability (DeSimone & Dolzmann 22 and Conti et al 23,24 ). As this model may not accurately reflect the changes in the microstructure over a large range of temperatures, we also consider an alternative model where the nematic elastomer is treated as a freely-jointed chain (e.g., Finkelmann et al 16 ).…”

“…Consider, for example, (24) 1 . For λ > 1, (24) 1 requires that λ < a 1/3 in the prolate phase a > 1. However, for 0 < λ < 1, (24) 1 requires λ > a 1/3 in the oblate phase a < 1.…”

Strain-induced polarization in non-ideal chiral nematic elastomers

“…The form of the polarization is rather unusual, with a very steep profile and non-continuous changes of gradient at the onset and end of director rotation. In reality, if a sample is stretched in this manner without applying the energy-lowering shear with the clamps, then the elastomer will split into stripes (see Conti et al (2002) for theory or Finkelmann et al (1997) for experiment) each of which undergo opposite shear so that the average shear of the sample is zero. These stripes will have opposite polarization.…”