Semisoft Nematic Elastomers and Nematics in Crossed Electric and Magnetic Fields

Abstract

Nematic elastomers with a locked-in anisotropy direction exhibit semi-soft elastic response characterized by a plateau in the stress-strain curve in which stress does not change with strain. We calculate the global phase diagram for a minimal model, which is equivalent to one describing a nematic in crossed electric and magnetic fields, and show that semi-soft behavior is associated with a broken symmetry biaxial phase and that it persists well into the supercritical regime. We also consider generalizations beyond the minimal model and find similar results.

On the nonlinear stress-strain behavior of nematic elastomers – materials of two coupled preferred directions

“…We start our calculations by deriving an expression for the matrix R −1 , which describes the elastic rotational deformation of the polymer network. For this purpose, we introduce ansatz (12)- (14) into Eqs. (3) and (6).…”

“…Recently, a biaxial model has been proposed 14 to describe the results of the nonlinear stress-strain experiments. The two directions in the nematic SCLSCE are assumed to be given on the one hand by an internal stress imprinted into the material during the process of synthesis, and on the other hand by the external stress applied to the material during the stress-strain experiment.…”

Modeling elastic instabilities in nematic elastomers

“…For instance in a nematic LCE, any change in the magnitude of the nematic order parameter induces shape change, e.g. the isotropic-nematic phase transition induces strains of up to several hundred percent [3].Conversely, applied strain can also drive changes in orientational order, producing the fascinating phenomenon of semisoft elasticity [4]. In a classic experiment, Kundler and Finkelmann [5] measured the mechanical response of a monodomain nematic LCE thin film stretched along an axis perpendicular to the nematic director.…”

Thermomechanical modeling of the thermo-order–mechanical coupling behaviors in liquid crystal elastomers

“…The synthesis of a LCE and the initial configuration may affect its energy and deformation. Currently, there are a lot of papers about semi-soft elasticity and the free energy function (Ye et al, 2007;Biggins et al, 2008;Ye and Lubensky, 2009;Menzel et al, 2009). For the semisoft elasticity model with one preferential direction, director n, the similar method in Section 2 can be used to obtain the equilibrium equations.…”

“…By introducing such an additional direction, Menzel et al (2009) proposed a model for LCEs with two coupled preferred directions. Ye et al calculated the global phase diagram and tried to understand the semi-soft behaviors (Ye et al, 2007;Ye and Lubensky, 2009). In order to model the different order-mechanical coupling behaviors of LCEs, different methods are used.…”