Eur. Phys. J. E (2006) 20: 55-61
https://doi.org/10.1140/epje/i2005-10119-2

Regular Article

Frustrated structure of an anticlinic-like smectic-C phase

¹ Centro de Fısica da Matéria Condensada, Av. Prof. Gama Pinto 2, 1649-003, Lisboa Codex, Portugal
² Departamento de Fısica, Instituto Superior Técnico, Av. Rovisco Pais, 1049-001, Lisboa Codex, Portugal
³ Departamento de Fısica, IFIMUP, Faculdade de Ciências da Universidade do Porto, Rua do Campo Alegre 687, 4169-007, Porto, Portugal
⁴ Centre de Recherche Paul Pascal, CNRS, Av. A. Schweitzer, 33600, Pessac, France

^* e-mail: pedros@lince.cii.fc.ul.pt

Received: 1 August 2005
Accepted: 22 March 2006
Published online: 3 May 2006

Abstract

We present a polarising optical microscopy study of the low-temperature anticlinic-like tilted mesophase of the liquid-crystal compound octylphenyl-2-chloro-4-(p-cyano-benzoyloxy) (DB₈Cl). This mesophase has been described as a bilayer smectic structure in which the molecules within each layer are organised in an anticlinic way. The optical textures observed in samples with planar orientation show a double stripe pattern, with the lines aligned parallel to the rubbing direction, characteristic of a double periodic modulation of the refractive index of the material. The long-period modulation is temperature dependent and disappears for thin sample cells (< 5μm). The short-period modulation is nearly independent of the thickness of the cells. The experimental results are analysed in terms of a model which considers that there is a special distribution of the principal optical axis which may be in or out of the polariser-analyser plane. The observed periodic variation of the principal optical axis could not be interpreted in terms of the original structure proposed for this phase. DB₈Cl presents a structure formed by dimers that can be viewed as flexible bent-core-like molecules, showing similarities with phases found in banana-like systems, but exhibiting a much more complex structure.