Electro- and photoswitching of undulation structures in planar cholesteric layers aligned by a polyimide film possessing various values of the anchoring energy

ABSTRACT

It is known that the applying of the alternating electric field to a planar texture of cholesterics, at the certain ratio between the LC cell thickness d and the cholesterical helix pitch P, can give rise to the formation of uniform two-dimensional (2D) or one-dimensional (1D) structures (Helfrich–Hurault effect or the so-called undulation instabilities). In this manuscript, on the basis of the studies carried out in the article by B. Senyuk et al. (Proceedings of SPIE. 2005; 5936: 59360W01), the change in the ratio d/P, owing to the unwinding of the photosensitive cholesteric helix during UV exposure in the LC cell with a fixed thickness d, was achieved. As a photosensitive cholesteric liquid crystal, the mixture of the photosensitive chiral dopant 2-(4′-phenylbenzylidene)-p-menthane-3-one dissolved in the nematic E7 was used. Due to the decrease in a ratio d/P, different types of undulations, observed under the alternating electrical field, were switched by UV exposure. By means of UV exposure of a cholesteric, the sequential undulation transitions from 2D to two 1D (1D_║ and 1D_┴) were received. The influence of UV exposure and the value of the azimuthal anchoring energy on electro- and photoswitching of undulation instabilities were studied. In the case of the 1D_║ undulation structure having a controlled period of a grating both in alternating electric field and during UV exposure, the dependencies of jumps of the period and the diffraction efficiency of a cholesteric grating on the anchoring energy of alignment layers were examined.

GRAPHICAL ABSTRACT

KEYWORDS:

• Cholesteric liquid crystals
• photosensitive chiral dopant
• undulation instabilities
• anchoring energy
• cholesteric diffraction gratings

Acknowledgements

Author I.G. thanks W. Becker (Merck, Germany) for his generous gift of the nematic E7, A. Kratz (Merck, Germany) for her produce of the Licristal brochure, Prof. I. Gerus (Institute of Bio-organic Chemistry and Petrochemistry, NAS of Ukraine) for the kind provision of polymer ODAPI, Prof. O. Lavrentovich and his PhD student B. Li (Kent State University, USA) for gift of the polyimide PI2555 (HD MicroSystems, USA), scientific researcher P. Tytarenko (V. Ye. Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine) for the preparation of indium–tin oxide (ITO)-coated on glass substrates, field service specialist IV V. Danylyuk (Dish LLC, USA) for his gift of some laboratory equipment, Prof. L. Lisetski (Institute for Scintillation Materials of STC 'Institute for Single Crystals', NAS of Ukraine) and Dr. S. Lukyanets (Institute of Physics, NAS of Ukraine) for the helpful discussions.

Disclosure statement

No potential conflict of interest was reported by the author.