SOFT RUBBER ELASTICITY

Nematic elastomers, because of their internal orientational degree of freedom, have been predicted to possess some totally soft modes of distortion. Their free energy is predicted not td rise when certain strains lambda are imposed. We give explicit examples of such strains and then investigate whether these stress-free strains, more typical of liquids, remain soft when the network chains have compositional fluctuations. We conclude that random copolymer nematic elastomeric networks; are hardened very slightly to give moduli along the previously soft directions between 10(-8) and 10(-4) times that of the equivalent nonnematic rubber.