Electromechanical Properties of Smectic C Liquid Crystal Elastomers under Shear

Liquid crystal elastomers combine the electrical and optical properties of liquid crystals with the mechanical ones of polymer networks. In smectic C systems, doping with chiral mesogens induces the formation of domains with permanent electric dipole moment, which exhibit piezoelectric properties. Orientation of the mesogen in a uniaxial mechanical field and subsequent cross-linking produce a centrosymmetric morphology, where the piezoelectric effects are averaged out on a macroscopic length scale. The application of shear breaks the symmetry and induces the formation of a monodomain structure. In this study the measurements of the direct piezoelectric effect are compared with the recently published structural changes during stepwise shear. It is shown that the piezoelectric coefficient reaches its maximum at a certain shear angle that corresponds to the intrinsic smectic tilt angle. The complex electromechanical coefficient may vary up to a factor of 2 in a broad temperature, static mechanical stress and frequency range. The response of the system remains linear, the higher harmonics contributing no more than ∼10% in any case.