Eur. Phys. J. E 10, 143-151 (2003)
DOI: 10.1140/epje/e2003-00018-9

Rectangular to hexagonal columnar phase transition exhibited by a biforked mesogen

A.C. Ribeiro^{1, 2}, B. Heinrich¹, C. Cruz², H.T. Nguyen³, S. Diele⁴, M.W. Schröder⁴ and D. Guillon<sup>1

1</sup>  Institut de Physique et Chimie des Matériaux de Strasbourg (UMR 7504) , 23 rue du Loess, BP 20, 67037 Strasbourg, France
²  Centro de Física da Matéria Condensada - UL, Av. Prof. Gama Pinto, 1649-003 Lisboa, Portugal and IST-UTL, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
³  Centre de Recherche Paul Pascal, Domaine Universitaire, 33405 Talence, France
⁴  Univ. Halle Wittenberg, Inst. Phys. Chem., Muhlpforte 1, 06108 Halle, Germany

ribeiro@cii.fc.ul.pt

(Received 1st October 2002 Published online: 16 April 2003)

Abstract
We present the structural study of a biforked compound exhibiting a Col -Col phase transition. This study was performed by means of DSC, optical microscopy, X-ray diffraction, dilatometry and molecular modelling. The molecular packing within the two columnar mesophases of this compound is discussed. For the first time, it is shown that the clusters of adjacent molecules which form the elementary section of a column are tilted with respect to the columnar axis in the rectangular mesophase. From the whole set of experimental data, the number of molecules in a columnar section is found to be about 5 in the rectangular mesophase, and 4 in the hexagonal one. The transition between the two columnar mesophases is discussed with respect to its slow kinetics.

PACS
61.30.Cz - Molecular and microscopic models and theories of liquid crystal structure.
64.70.Md - Transitions in liquid crystals.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003