High resolution X-ray diffraction study of Smectic A - Smectic A phase transitions in a binary mixture of polar thermotropic liquid crystals

Abstract

With the help of the synchrotron radiation facility LURE, we have studied the following mesogenic phase sequence: Smectic A 1 (monolayered) ― fluid antiphase with a rectangular 2D lattice ― Smectic A 2 (bilayered), we have shown the existence of two ribbon phases with rectangular lattices of different symmetries. Besides the centred rectangular phase already described (S A ) in which the two kinds of antiphase domains have an equal weight, we have found a second phase with a simple rectangular lattice in which the relative weight of the two kinds of domains varies with temperature until the S Ad 2 phase is reached. In the centred rectangular phase, the in-layer periodicity increases with decreasing temperature while it remains constant in the simple rectangular phase. The transition temperature between these two phases exhibits a hysteresis of a few degrees Etude en utilisant le rayonnement synchrotron de LURE, de la sequence de phases mesogenes suivante: smectique A 1 (couches monomoleculaires) ― antiphase fluide a reseau rectangle bidimensionnel ― smectique A 2 (couches bimoleculaires). Existence de deux phases en ruban a reseau rectangle de symetrie differente