Comparison between the switching dynamics of homeotropic and planar cells of chiral smectic-C liquid crystals

Abstract

The molecular dynamics during the switching of homeotropic and planar cells of chiral smectic-C liquid crystals has been investigated using electrooptic measurements and second-harmonic-generation interferometry. Two ferroelectric liquid crystals with great differences in their molecular structures have been studied. It has been found that the molecular motion is rather different depending on the type of cell used. For planar cells, the azimuthal rotation of the molecules is limited within half the smectic cone and the molecules rotate in opposite directions in the two halves of the chevron structure. In contrast, for homeotropic cells there is no chevron structure and a uniform macroscopic optical indicatrix can be defined all over the sample during the whole switching process. However, the molecular reorientation takes place within numerous microdomains of size smaller than the optical wavelength. There are two types of microdomains that occur with different probabilities depending on the material. Within each domain the molecules rotate in opposite directions, and the molecules describe a complete cone during a whole switching period.