J. Phys. II France
Volume 5, Numéro 7, July 1995
Page(s) 927 - 935
DOI: 10.1051/jp2:1995221
J. Phys. II France 5 (1995) 927-935

From Incommensurability to Commensurability in Smectic Phases for a Series of Dimesogenic Liquid Crystals

F. Hardouin1, M.F. Achard1, Jung-Il Jin2 and Yong-Kuk Yun2

1  Centre de Recherche Paul Pascal, Université Bordeaux I, avenue A. Schweitzer, 33600 Pessac, France
2  Department of Chemistry, College of Sciences, Korea University, Seoul 136-701, Korea

(Received 9 February 1995, accepted 5 April 1995)

Genuine incommensurate smectic A phases were recently discovered, among the rich polymorphism of a new dimesogenic liquid crystal compound (KI5). In the present paper, we examine the role played by molecular parameters in the existence of such incommensurate state. In a series of several homologues of KI5, we find that two smectic modulations exist in agreement with the phenomenological model of "frustrated smectics". The condensation of one or the other of these modulations and their coexistence appear to be closely related to the length of the flexible spacer linking the two mesogenic moieties. We observe that only for intermediate spacer length, the elasticity of the system allows the occurrence of incommensurate SA phases.

© Les Editions de Physique 1995