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S. A. Syrbu^1,2,  Z. A. Kudryashova^3,4,  L. A. Nosikova^3,4,  E. I. Efremova³, M. R. Kiselev⁴

Author affiliations
¹Ivanovo State University, Inorganic and Analytical Chemistry Dept.,
Russia, 153025, Ivanovo, Ermak street, 39.
²Ivanovo Institute of the State Fire Service
Stroitelei pr. 33, Ivanovo, 153040 Russia. 
E-mail: syrbue@yandex.ru
³Lomonosov Moscow State University of Fine Chemical Technologies
119571 Moscow, Russia, prospect Vernadskogo 86
⁴A.N. Frumkin Institute of Physical chemistry and Electrochemistry RAS
31, Leninsky prospect, Moscow, 199071 Russia

Abstract
The p-n-heptyloxybenzoic acid(I) – p-n-undecyloxybenzoic acid (II) system studied by polarizing optical microscopy, differential scanning calorimetry and dilatometric methods. Coordinates of the invariant equilibrium were obtained. Temperature and concentration dependencies of volume properties were analyzed. It was found that in the system there are two nematic and two smectic subphases. For the composition with the ratio of components 2(I): 1(II) the density and its derivatives values are extremal, indicating the formation of acid associates in the system.

Keywords: liquid crystals, p-n-alkyloxybenzoic acids, polarizing optical microscopy, differential scanning calorimetry, polythermal dilatometry, nematic subphases, associates, density, molecular packing coefficient, excessive molar volume.