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.