THE ROLE OF GOLDSTONE MODE AND ELECTROCLINIC EFFECTS IN ELECTROMECHANICAL RESPONSES OF CHIRAL SMECTIC-C LIQUID-CRYSTALS

We studied the electromechanical effects of smectic C sandwich cells. Some earlier results are reviewed and new measurements are reported o f the motions of the cover glass as a function of frequency and voltag e for different textures (chevron, striped add uniform bookshelf). The analysis of the observations show that there are two mechanisms which dominate the linear electromechanical effects: the coupling between f ield induced director rotation, (Goldstone mode) and flow and the elec troclinic effect. The Goldstone mode is most strongly excited in unwou nd smectic bookshelf or chevron textures when the spontaneous polariza tion is parallel to the substrate. It causes a horizontal motion of th e cover plate. The electroclinic effect induces a vertical motion. It is most strongly excited in an unwound bookshelf or chevron texture wh en the polarization is vertical. The mechanical responses show resonan ces in the kilohertz frequency range, in particular for the vertical r esponses. We found that the resonances correspond to eigenmodes of the glass plates.