The Role of Goldstone Mode and Electroclinic Effects in Electromechanical Responses of Chiral Smectic C Liquid Crystals

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Abstract
We studied the electromechanical effects of smectic C* sandwich cells. Some earlier results are reviewed and new measurements are reported of the motions of the cover glass as a function of frequency and voltage for different textures (chevron, striped and uniform bookshelf). The analysis of the observations show that there are two mechanisms which dominate the linear electromechanical effects: the coupling between field induced director rotation (Goldstone mode) and flow and the electroclinic effect. The Goldstone mode is most strongly excited in unwound smectic bookshelf or chevron textures when the spontaneous polarization is parallel to the substrate. It causes a horizontal motion of the cover plate. The electroclinic effect induces a vertical motion. It is most strongly excited in an unwound bookshelf or chevron texture when the polarization is vertical. The mechanical responses show resonances in the kilohertz frequency range, in particular for the vertical responses. We found that the resonances correspond to eigenmodes of the glass plates.