Models for Nematic Rubber Elasticity

Modifications of the conventional Gaussian elastomer theory were proposed that include short range nematic interactions. These an- 

If / and /x are the effective step lengths (monomer length) for the random walks parallel and perpendicular to the ordering direction (in the isotropic phase / =/x= o) respectively, and under the assumption that the deformation occurs without a change of volume, the following relation is obtained for the elastic component of the free energy in the nematic phase 

Warner et al. [88,89] give a full description of the free energy and recover, by minimization, the spontaneous strain and the mechanical critical point. They also show that, if the network is crosslinked in the nematic phase, a memory of-the nematic state is chemically locked. This causes a rise in the nematic-isotropic phase transition temperature compared with the uncrosslinked equivalent. After crosslinking in the isotropic state, the transition temperature (on the contrary) is lowered. 

The same idea of nematic interactions favoring the distortion of the chains is also the basis of phenomenological descriptions. Jarry and Monnerie [86] and Deloche and 

Samulski [90, 91] described these interactions in the mean field approximation by an additional intermolecular potential from the classical theory of rubber elasticity. A similar expression is proposed for the elastic free energy. 

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