Study of SA Phase Structure Using Dielectric Relaxation

The results of a study of dielectric relaxation for several mesomorphous substances are presented. These compounds allow us to obtain information on the following phases: —the nematic phase-partially bilayer (SAd), bilayer (SA2) and monolayer (SA1) smectic A phases-the antiphase smectic A (SÃ). The measurements were performed with the electric field parallel to the director. The absorption observed is due to the reorientation motion of the molecule round an axis perpendicular to its longitudinal axis. The activation energy W of this movement was measured for all phases. Results show clearly that for these compounds W SAd < W N, W SA1 ∼ W N ∼ W SÃ and W SA2 > W N. In each case an explanation has been suggested to interpret these changes in the activation energy. This points out the possibility of showing the existence of some SA phases using dielectric relaxation.