Dielectric and X-ray Studies of Eleventh and Twelfth Members of Two Isothiocyanato Mesogenic Compounds
M. Jasiurkowskaa, A. Budziaka, J. Czub b and S. Urbanb
a H. Niewodniczański Institute of Nuclear Physics, Polish Academy of Sciences, Radzikowskiego 152, 31-342 Kraków, Poland
b Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland
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Received: 11 09 2006; in final form: 27 11 2006;
Results of the dielectric and X-ray studies of the long-alkyl-chain members (n=11, 12) of two homologous series: nBT (4-n-alkyl-4'-isothiocyanato-biphenyl) and nCHBT (4-trans-4'-n-alkyl-cyclohexyl-isothiocyanato-benzene) in their liquid crystalline phases are presented. These compounds exhibit different polymorphisms: the nematic phase for nCHBTs and the smectic E and smectic A phases for nBTs. The dielectric measurements were performed in a wide frequency range of 1 kHz-3 GHz. The layer thickness in the smectic E and smectic A phases and the orthorhombic unit cell parameters of the smectic E phase were determined using the small angle X-ray diffraction method. In the smectic E phase the layer-thickness-to-molecular-length ratios are found to be close to 1. The corresponding ratios observed for the smectic A phase of nBTs are considerably higher (≈1.24), which indicates that an alternating head-to-tail arrangement of molecules in the layers is favored. The rotational dynamics of molecules in the smectic E phases is discussed in relation to their packing in a unit cell.
DOI: 10.12693/APhysPolA.110.795
PACS numbers: 61.10.Eq, 61.66.Hq, 64.70.Md, 77.22.-d, 77.22.Gm