Liquid crystal elastomers with mechanical properties of a muscle

Free-standing anisotropic side chain liquid crystalline elastomer films hav e been prepared using mesogens with laterally affixed polymerizable side ch ains. We present data on two networks: one containing the monomer of 4'-acr yloyloxybutyl 2,5-(4'-butyloxybenzoyloxy)benzoate and another from a 50/50 mol % mixture of the above with 4'-acryloyloxybutyl 2,5-di(4'-pentylcyclohe xyloyloxy)benzoate. The cross-linking was achieved using 10 mol % of 1,6-he xanediol diacrylate. The calculated cross-linking density, as determined fr om the Young's modulus, was in the 10(-5) mol/cm(3) range. Thermoelastic re sponses show strain changes through the nematic-isotropic phase transition to be 30-45%. The order parameters of the oriented films were determined fr om the dichroic ratio of IR absorption at 3343 cm(-1) to the inplane aromat ic stretching overtone of the LC mesogen core. The variation of the order p arameter with temperature scales similar to the strain changes at constant stress. Isostrain studies, conducted through the nematic to isotropic phase transition, show that the two networks behave as true elastomers with sign ificant differences in the force developed. Dynamic shear measurements near the nematic to isotropic phase transition region show that the mechanical relaxation peak appears above 100 Hz, and that viscoelastic relaxations are minimal in the nematic to isotropic phase transition region below 5-10 Hz.