Molecular dynamics in chiral and non-chiral liquid crystalline systems

For the chiral systems, the molecular dynamics were studied in view of the phase transitions. In this paper, we present the studies of the high frequency relaxation processes for two chiral substances by TDS method in the frequency range from 10 MHz to 10 GHz. Especially the SmA*-SmC* transition is of great interest as there are some theoretical models predicting distinct changes of the critical frequencies and dielectric increments. The high frequency results are in agreement with the experimental results for other systems which show clearly that the reorientation of molecules around the long axis takes place in ferroelectric SmC* phases, and there is no distinct change of the dielectric parameters at the SmA*-SmC* transition. It was found, however, that the distribution parameter of relaxation times is enhanced at the SmA*-SmC* transition. The dielectric results obtained for nonchiral thioesters exhibiting the sequence of phases: N-SmA-SmC, show that the principal molecular motions (reorientations around the long and short axis) are not slowed down at the phase transitions.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.