Frustrated structure of an anticlinic-like smectic-C phase.
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 (< 5 microm). 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.
Sebastião
P J
PJ
Centro de Física da Matéria Condensada, Av. Prof. Gama Pinto 2, 1649-003, Lisboa Codex, Portugal. pedros@lince.cii.fc.ul.pt
Simeão Carvalho
P
P
Chaves
M R
MR
Nguyen
H T
HT
Ribeiro
A C
AC
D003460:Crystallization; D008956:Models, Chemical; D008968:Molecular Conformation; D044367:Phase Transition; D010636:Phenols / Q000737:chemistry*; D011108:Polymers / Q000737:chemistry*; D013314:Stress, Mechanical
D010636:Phenols; D011108:Polymers; C422409:liquid crystal polymer; C474055:octylphenol