X-ray diffraction, optical birefringence, dielectric and phase transition properties of the long homologous series of nematogens 4-(trans-4′-n-alkylcyclohexyl) isothiocyanatobenzenes
The temperature dependence of density, refractive indices, apparent molecular length and intermolecular distance of 11CHBT, are reported, together with the static dielectric permittivities, ε∥, ε⊥, εiso of 11CHBT and 12CHBT; the effect of chain length on various physical properties of the CHBT series is also discussed. All the temperatures Tm, TNI and TNCr show an odd-even (OE) effect, but transition enthalpies ΔHm and ΔHC show no such behaviour. Tm, TNI, TNCr and ΔHm are found to increase with chain length, while ΔHC shows a maxima at n = 6. At the common reduced temperature T* = 0.98 TNI, the density of the compounds are found to decrease with increasing chain length while the polarizability parameters αe, αo and α ¯ increase. However, the volume expansion coefficient, polarizability anisotropy and normalized polarizability anisotropy show a distinct OE effect. Similarly, ne decreases smoothly with chain length but no and Δn show an OE effect like ε⊥ and Δε. The ratio ln〈P2〉/ln〈P4〉 remains closer to Faber theory than MS theory. Effective dipole moments are found to be approximately constant in the series; antiparallel association is observed in all the members. Kirkwood correlation factors g⊥ and Δg are found to exhibit an OE effect like ε⊥ and Δε, but g∥ and ε∥ show no such effect. The effects of substitution in the core and end polar group on these properties are also discussed.
Document Type: Research Article
Affiliations: 1: Department of Physics, University of North Bengal, Siliguri, Darjeeling--734 430 (W.B.), India 2: Institute of Chemistry, Military University of Technology, Warsaw, Poland
Publication date: 01 April 2003
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