J. Phys. II France
Volume 2, Numéro 12, December 1992
Page(s) 2197 - 2206
DOI: 10.1051/jp2:1992260
J. Phys. II France 2 (1992) 2197-2206

Columnar to nematic mesophase transition in mixtures of rhodium or copper soaps with hydrocarbon solvents

M. Ibn-Elhaj1, D. Guillon1, A. Skoulios1, A. M. Giroud-Godquin2 and J.-C. Marchon2

1  Institut de Pysique et Chimie des Matériaux de Strasbourg, Groupe des Matériaux Organiques, ICS, 6 rue Boussingault, 67083 Strasbourg Cedex, France
2  Laboratoire de Chimie de Coordination URA 1194 CNRS, DRFMC/SESM, Centre d'Etudes Nucléaires de Grenoble, B.P. 85X, 38041 Grenoble Cedex, France

(Received 24 March 1992, revised 20 July 1992, accepted 14 September 1992)

This paper describes observations of the mesomorphic behaviour of mixtures of rhodium eicosanoate or copper dodecanoate with solvents such as toluene, decahydronaphthalene, and (+) camphene. The mesophase found with these compounds at high temperatures turns from columnar to nematic when the weight fraction of the solvent (toluene, decahydronaphthalene is increased beyond a value of about 50 %. The binary phase diagram of the copper compound with toluene was experimentally determined using polarizing optical microscopy, differential scanning calorimetry and X-ray diffraction. The novel feature of the nematic phase is that the basic physical object which align parallel to the nematic director are not individual molecules, but columns of molecules (one-dimensional supramolecular assemblies) which have lost the long-range lateral positional order characteristic of the columnar mesophase. These observations are discussed on the grounds of recent theoretical calculations. Cholesteric-like textures are observed for mixtures of rhodium eicosanoate with the chiral solvent (+) camphene.

© Les Editions de Physique 1992