Study of phase behavior in a system of linear hydrogen-bonded carboxylic acid homologues

Abstract

The system of hydrogen-bonded liquid crystals formed from binary mixtures p-n-heptyloxybenzoic (I) acid and p-n-undecloxybenzoic (II) acid has been investigated by polarizing optical microscopy, differential scanning calorimetry, X-ray diffraction, and scattering and dielectric measurements. The T–X phase diagram was obtained for this system. All mixtures show enantiotropic smectic and nematic phases. The crystalline phase represents a (α, β) solid solution. At the 2:1 ratio of I to II, an intermediate phase – co-crystal γ – is formed. The co-crystal γ possesses a much wider mesophase range than the corresponding initial components. In contrast to mixtures based on the solid solutions having a positive anisotropy, the co-crystal shows a negative dielectric anisotropy in the mesophase.

Keywords:

• alkoxybenzoic acids
• hydrogen-bonded
• liquid crystals
• phase diagram

Acknowledgments

We are grateful to an anonymous reviewer for the useful comments.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by Goszadanie – 2014/114 project code 150 (Ministry of Education and Science of the Russian Federation).