MODULATED STRUCTURES OF THE SMECTIC-C-ASTERISK PHASE IN FREESTANDING FILMS WITH HIGH SPONTANEOUS POLARIZATION

The stripe instability of smectic-C* free-standing films with high spontaneous polarization is studied experimentally and theoretically. By variation of the temperature, the number of smectic layers, and the spontaneous polarization in chiral-racemic mixtures, different structural states develop in the film. Temperature-number-of-layers phase diagrams of the smectic-C* structural states with spontaneous polarization as a parameter have been measured. The critical number of layers and spontaneous polarization for the textural transformations have been determined. A stripe state has also been observed in an antiferroelectric phase. A mechanism for stripe formation is proposed that considers the stripes occuring as flexoelectric instabilities in an electric field inherently produced by the film. The proposed theoretical model gives a qualitatively good explanation of the experimental data. © 1995 The American Physical Society.