The effect of spontaneous polarization on two-dimensional elasticity of smectic liquid crystals

The influence of polarity on orientational elasticity and on structures formed in the director field is studied in free-standing smectic films. Periodic stripe patterns and 2π-walls in a magnetic field are investigated. Measurements are performed on a nonpolar racemic mixture, on an optically pure ferroelectric compound, and in mixtures with different concentrations of the chiral isomers of opposite signs. The structure of periodic stripes changes drastically with the polarity of the film. The ratio of the bend K _B and splay K _S elastic constants for smectic films is determined as a function of polarization from the structure of periodic stripe patterns and 2π-walls. We find that the elastic anisotropy K _B /K _S increases essentially with increasing the polarity of the film. Changes of the elasticity and the structure of periodic stripes are explained by polarization charge effects.