Dielectric study of the SAd - SA2 phase transition of new thermotropic liquid crystals

In this paper, we will report on the study, in a large frequency range, of some new thermotropic liquid crystals whose phase sequence is made up of S Ad -S A2 -type transitions. At this transition, we observe a dielectric behaviour appreciably different from one sample to another: thre is variation in the dielectric static anisotropy and variation int he activation energy of the «flip-flop» rotation in the parallel measurement direction. Our results confirm those obtained elsewhere by means of other investigation techniques like microscopic observations, DSC experiments and X-ray data Etude experimentale des permittivites statique et dynamique sur une large bande de frequences, pour plusieurs cristaux liquides presentant ce polymorphisme des phases smectiques. Suivant les composes, observation de la variation l'anisotropie dielectrique statique ou de l'energie d'activation du mouvement de basculement dans la direction parallele de mesure, lors de la transformation de phase