Molecular Orientation and Switching Behavior in Antiferroelectric Liquid Crystals Studied by Polarized Raman Scattering

The orientational distribution in SmA, the switching behavior in SmC * , and the molecular orientation of SmC A * have been investigated by means of polarized Raman scattering due to the C–C stretching of phenyl rings in two antiferroelectric liquid crystals. The scattered intensities, I Z Z (ω) and I Y Z (ω), have been measured between crossed and parallel polars as a function of rotation angle, ω, of homogeneously aligned cells about their surface normal. The order parameters, < P 2 > and < P 4 >, and then the orientational distribution function in SmA were obtained by utilizing the method of information entropy. The electric-field-induced reorientation was observed in the rotation angle dependence: I Z Z (ω)∝cos 4 (ω±Θ), where Θ is the tilt angle of SmC * . The characteristic rotation angle dependence obtained in SmC A * was described as I Z (ω)∝{cos 4 (ω+Θ)+cos 4 (ω-Θ)}/2. This result supports the molecular orientation of SmC A * so far proposed that the molecules in adjacent layers tilt in the opposite senses.