Converse piezoelectricity of fluid ferroelectric nematic liquid crystals

Recent studies demonstrated converse piezoelectricity in ferroelectric nematic (N_F) liquid crystals, which are 3-dimensional polar anisotropic fluids. [1] Here we study the effect in a home-made room temperature N_F material in three directions. By symmetry considerations, one of the three directions we expect a signal, while in the other two we do not. Indeed, we found the largest signal when the shear direction is along the director and the signal is perpendicular to it. In this direction the observed coupling constant is , much higher than the coupling constant in crystalline ferroelectrics. In the other two (forbidden) directions the signals were indeed much smaller, but not zero due to imperfect alignments and measuring errors. Understanding the linear electromechanical response of fluid N_F materials is important for wide-range of applications ranging from mechanical energy harvesting, developing fluid actuators, micro positioners, and electrically tunable optical lenses.