Piezoelectricity in ferroelectric liquid crystalline elastomers

The direct and inverse piezoelectricity in single crystal ferroelectric liquid crystalline elastomers was measured by means of purpose-made experimental setups. As expected the observed effects depended strongly on temperature and the strength of the applied alternating electric field; additionally they could be strongly enhanced by a superimposed direct current electric field. The latter resulted from a molecular amplification of the polarization vector of the single smectic layers by inducing a rotational bias of the lateral distribution of the polar groups of the mesogens. This resulted in a pronounced magnification of the (macroscopic) piezoelectric effect. Backed also by X-ray measurements, a model is suggested, which interprets the observed piezoelectricity as caused by a field-induced change of the inclination of the tilted smectic layers. The strength of the observed electromechanical effects compares well with or exceeds that of classical materials, such as barium titanate or lead–zirconate–titanate or the polymer polyvinylidene fluoride.