Determination of Bend to Splay Elastic Constant Ratio (K3/K1) of Several Nematogens and Applicability of Spherocylindrical Model
作者:
M.K. Das,
R. Paul,
期刊:
Molecular Crystals and Liquid Crystals Science and Technology. Section A. Molecular Crystals and Liquid Crystals
(Taylor Available online 1995)
卷期:
Volume 259,
issue 1
页码: 13-21
ISSN:1058-725X
年代: 1995
DOI:10.1080/10587259508038669
出版商: Taylor & Francis Group
关键词: nematogen;elastic constants;spherocylindrical model
数据来源: Taylor
摘要:
In the present work we have tried to test the theory of elastic constants of nematogens given by Priest, assuming Spherocylindrical shape of the molecules. The bend (K3) to splay (K1) elastic constant ratios of four closely related nematic liquid crystals, having cyclohexane carboxylate core, have been determined by us using Freedericksz transition in a magnetic field. The length and width of the molecules and the order parametersP2andP4, required for the theoretical calculations, have been estimated from our earlier X-ray studies on these compounds. The experimental values of the ratioK3/K1for three of these compounds agree quite well with those calculated from the Spherocylindrical model. The fourth nematogen, for which the agreement is poor, shows anomalous temperature variation of density and hence the rigid Spherocylindrical model is not probably applicable to it. We have also measuredK3/K1forn-pentyl cyanobiphenyl (5CB), and have shown that the X-ray experimental data implies thatP4is positive even near the nematic-isotropic transition temperature for 5CB, which is at variance with some experimental Raman scattering results. Finally, theK3/K1ratios for pentyloxy cyanobiphenyl (5OCB) at different temperatures obtained experimentally by Bradshawet al. have been compared with those calculated from Spherocylindrical model using our X-ray data.
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