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Liquid Crystals and their Application
Russian Journal

Zhidkie kristally i ikh prakticheskoe ispol'zovanie

Жидкие кристаллы и их практическое использование

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Rus Eng


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Zhidk. krist. ikh prakt. ispol'z. = Liq. Cryst. and their Appl., 2014, 14 (3), 27—34.

Electrooptic Properties of Isotropic Melts of Smectic 4-n-Alkyl-4'-Cyanobiphenyls

S. G. Polushin, A. V. Zakhryapa, V. B. Rogozhin, G. E. Polushina, A. A. Shevlyagin, M. E. Palenov, I. P. Kolomiets, A. V. Komolkin, E. I. Rjumtsev

Author affiliations
Saint-Petersburg State University,
Ulianovskaya, 1, 198504 Saint-Petersburg, Petrodvoretc, Russia. 

The electric birefringence in the isotropic melts of two smectic nCB homologues with n = 10, 12 was investigated. Measurements were performed above clearing temperature in a wide temperature range of about 60 degrees with an experimental error of less than 1 %. It is shown that the temperature dependence of the reciprocal of the Kerr constant in the isotropic melt of 10CB and 12CB liquid crystals had the form 1/~(T–T*), where T* is a temperature of virtual phase transition of the second order and it allows to make a description of the electro-optical properties of the isotropic melt by the Landau – de Gennes model with orientation and coordination order parameters. It was found that in the isotropic state a sharp change of electrooptic properties takes place, whereby the dependence 1/~(T*–T) is approximated by two straight lines with different slopes. This fact, as well as availability for each of the studied liquid crystals of two temperature values T* is caused by a structural transition in the isotropic phase. It can be assumed that the transition in the smectic liquid crystals 10CB and 12CB occurs between the low-temperature melt, characterized by short-range orientation and coordination orders and the high temperature melt, which retains only the short-range orientation order.

Keywords: Kerr effect, isotropic phase, smectic

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