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The European Physical Journal B
ISSN: 1434-6028 (printed version)
ISSN: 1434-6036 (electronic version)
Abstract Volume 1 Issue 4 (1998) pp 503-512
Structural and optical investigations of $\mathsf{ TGB_A}$ and $\mathsf{ TGB_C}$ mesophases exhibiting cylindrical and cone-like domain textures
A.C. Ribeiro (1), L. Oswald (2), J.F. Nicoud (2), D. Guillon (2) (a), Y. Galerne (2)
(1) Centro de Fisica da Matéria Condensada (U.L.), avenida Prof. Gama Pinto 2, 1699 Lisboa Codex, Portugal
(2) Institut de Physique et Chimie des Matériaux de Strasbourg, Groupe des Matériaux Organiques, 23 rue du Loess, 67037 Strasbourg Cedex, France
Received: 16 June 1997 / Revised: 17 October 1997 / Accepted: 20 November 1997
Abstract: The characterization by optical microscopy, X-ray diffraction and differential scanning calorimetry of two new liquid crystalline compounds is presented. The compounds under consideration incorporate in their molecules two chiral centres (one asymmetric carbon and one asymmetric sulphur of a sulphinate group). While the carbon chirality is fixed in the R configuration the sulphur chirality may be either in the S or in the R configuration. A ${\rm TGB_A}$ mesophase in a large temperature domain is evidenced for one of the two diastereomers, while both ${\rm TGB_A}$ and ${\rm TGB_C}$ mesophases are observed in a similar temperature domain for the other one. For both diastereomers and in both mesophases it is possible to observe the coexistence of two different types of optical textures, namely planar cholesteric textures and developable domains. The latter are coiled in a different way than proposed in an earlier publication. More precisely, they form cylindrical or cone-like domains with double-twist properties as observed in the blue phases. The pitch of the helix in the TGB mesophases is evaluated by means of optical reflection observations in samples exhibiting the planar cholesteric textures. For both diastereomers it is also possible to evaluate structural parameters related to the organization within the ${\rm TGB_A}$ mesophases. Finally, the induced phase transition ${\rm TGB_C}$-${\rm S_{C^\ast}}$ is studied by the application of an AC electric field.
PACS. 61.30.-v Liquid crystals
(a) email: guillon@michelangelo.u-strasbg.fr
Online publication: March 19, 1998
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