Influence of polar dopant on internal configuration of azoxybenzene nematic-in-water droplets

ABSTRACT

We report the study of optical textures and director configurations within nematic-in-water microdroplets of the liquid-crystalline mixtures based on azoxybenzene and cyanobiphenyl (as a polar dopant). Both pure azoxybenzene and polar dopant materials exhibited bipolar configuration within liquid-crystalline droplets, whereas their mixtures at appropriate concentrations spontaneously formed radial droplets. It was found that increasing of the dopant’s concentration resulted in the forward tangential-homeotropic and reentrant homeotropic-tangential anchoring transitions. We also triggered bipolar-to-radial structural transition by UV irradiation providing trans-cis isomerisation of nematogens. Critical irradiation time needed for radial configuration formation was found to decrease with concentration of polar dopant. Mesoscoping modelling is proposed to explain main experimental results. The presented data are discussed for chemical and biological sensing applications.

Graphical Abstract

KEYWORDS:

• Liquid crystals
• azoxybenzene
• polar dopant
• microdroplets
• director configuration
• UV irradiation
• trans-cis isomerisation
• structural transformation

Acknowledgement

A.I. gratefully acknowledges the help of Ekaterina Gongadze. A.V.D. acknowledges V.S. Bezborodov for useful discussion.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was partially supported by the Ministry of Education and Science of the Russian Federation [Grant No. 3.1921.2014/K and Grant of the President of Russia for young scientists No. MK-4886.2016.2] and by the Russian Foundation for Basic Research [Grant No. 15-32-21143]. S.K. acknowledges the financial support from the Slovenian Research Agency [research core funding Nos. P1-0099 and P2-0232].