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Phase equilibria in 4-pentyloxybenzoic acid - long-chain n-alkane systems

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Objective. The work’s objective is to develop methods for the thermodynamic modeling of systems of liquid crystal - organic solvent.

Methods. Four binary systems of nematic 4-pentyloxybenzoic acid (5OBA) with n-alkanes (hexadecane, octadecane, icosane, and docosane) were investigated via thermal analysis methods (differential thermal analysis, polarization microscopy, visual polythermal analysis, and the polytherm solubility method). The accuracy in determining phase transitions temperatures is within 0.3 K. To describe the phase equilibria, models based on the Hildebrand and Hansen solubility parameters were used. Hansen solubility parameters were estimated using the Stefanis scheme. Hildebrand solubility parameters, molar volumes, and vaporization enthalpies were calculated using a group contribution scheme.

Results. Phase equilibria in the systems of 5OBA with n-alkanes were studied. Four T-x diagrams were obtained by thermal analysis methods, coordinates of invariant points (eutectics and metatectics) were determined in the systems. A linear dependence of the metatectic coordinate (х1 is a fraction of 5OBA, mol. %) on the number of C atoms in the alkane (N) was established: x1 = -0.3131 x N + 85.467. Solubility polytherms of 5OBA with solvents of different polarity were obtained: n-alkanes (hexane, octane), cyclohexane, aromatic compounds (benzene, toluene, and o-xylene), chlorobenzene, ethyl acetate, acetone, 1,4-dioxane, alcohols (propan-2-ol, propan-1-ol, butan-1-ol), and acetonitrile. The dependence of 5OBA’s solubility on the difference in the solubility parameters of the components and the distance Ra was established.

Conclusions. The model for regular solutions based on solubility parameters allows us to calculate the solubility polytherms of mesogens and to select solvents for the purification of mesogens by the mass crystallization method. The best solubility of 4-pentyloxybenzoic acid at 298 K appears in chlorobenzene.

About the Authors

V. O. Seregin
MIREA - Russian Technological University (M.V. Lomonosov Institute of Fine Chemical Technologies)
Russian Federation

Vladimir O. Seregin - Postgraduate Student, Department of Physical Chemistry.

86, Vernadskogo pr., Moscow 119571

S. M. Pestov
MIREA - Russian Technological University (M.V. Lomonosov Institute of Fine Chemical Technologies)
Russian Federation

Sergei M. Pestov - Dr of Sci. (Chemistry), Professor of the Ya.K. Syrkin Department of Physical Chemistry, Scopus Author ID: 6507847129; ResearcherID: G-9361-2017.

86, Vernadskogo pr., Moscow 119571

R. M. Zubairov
MIREA - Russian Technological University (M.V. Lomonosov Institute of Fine Chemical Technologies)
Russian Federation

Rustam M. Zubairov – Student.

86, Vernadskogo pr., Moscow 119571


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Supplementary files

1. Fig. 6. Solubility polytherms of 5OBA: – n-hexane, – n-octane, – cyclohexane, – benzene, – toluene, – propan-1-ol, – ethyl acetate.
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Seregin V.O., Pestov S.M., Zubairov R.M. Phase equilibria in 4-pentyloxybenzoic acid - long-chain n-alkane systems. Fine Chemical Technologies. 2019;14(6):66-75.

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