Microscopic ordering in smectic phases of liquid crystals

Abstract

Orientationa order in smectic phases of a ferroelectric liquid-crystalline material 4'-(2S,3S)-2″-chloro-3″-methylpentanoyloxyphenyl-4-decyloxy thiobenzoate, abbreviated 10.S.C1Isolleu, was examined by IR absorption spectroscopy. Oriented samples were prepared in both bookshelf and homeotropic alignment geometry. Several stronger IR vibrations were selected characterizing different parts and orientations of the molecules. Results show that the molecular tilt of the core parts of the molecules changes very little from the S A to the S C * phase implying that the core parts of the molecules are already tilted in the S A phase. Axes of the core parts, that are disordered on a cone in the S A phase, start to align with each other but remain on this cone on lowering the temperature into the S C * phase. The model agrees with some previous results On a etudie par spectroscopie d'absorption infrarouge l'ordre orientationnel dans les phases smectiques d'un materiau cristal liquide ferroelectrique, le decyloxy-4-thiobenzoate de [(2S,3S)-chloro-2-methyl-3-pentanoyloxy]-4'-phenyle, en abrege 10.S.C1Isoleu. Deux types d'echantillons orientes, l'un homeotrope, l'autre en configuration Clark-Lagerwall, ont ete prepares et plusieurs bandes intenses en infrarouge, caracteristiques des differentes parties et orientations des molecules, ont ete choisies. Les resultats montrent que l'inclinaison des parties centrales (cœurs) des molecules varie tres peu de la phase S A a la phase S C *, ce qui implique que les cœurs des molecules sont deja inclines dans la phase S A . Leurs axes, qui sont desordonnes sur un cone dans la phase S A , s'alignent mais restent sur ce cone quand on passe en phase S C * en abaissant la temperature. Ce modele est en accord avec quelques resultats anterieurs