Influence of the anchoring energy on jumps of the period of stripes in thin planar cholesteric layers under the alternating electric field

Abstract

Experimental studies of the dynamics of jumps of the period of stripes (PS) for the electrically induced ‘fingerprint’ texture of thin planar cholesteric layers are carried out for various values of the anchoring energy of substrates of liquid crystal (LC) cells. The nematic LC E7 doped by ZLI-3786 (R-811, Merck, Darmstadt, Germany) at a concentration 1.5 wt.% was used as the induced cholesteric with the helix pitch 5 µm. The ratio between the cell thickness and the cholesteric pitch was approximately 1.6. To study the influence of the anchoring energy W on jumps of the PS in the electric field, two polymers (oxidianiline-polyimide and polyvinyl-cinnamate) for the planar alignment of cholesterics were used. The anchoring energy of surfaces of polymers changes under the exposure to UV light. Experimentally, it was shown that jumps of the PS significantly depends on the value of the anchoring energy: (a) for the strong surface anchoring, jumps of the PS are observed; (b) for the sufficiently weak anchoring, no jumps are observed. The phenomenon of hysteresis of jumps of the PS is experimentally found when the electric field changes in the opposite direction.

Keywords:

• hysteresis
• cholesteric liquid crystals
• diffraction gratings
• anchoring energy

Acknowledgements

The author thanks W. Becker (Merck) for his generous gift of the nematic E7 and chiral dopant R-811, Prof. I. Gerus for the kind provision of ODAPI and PVCN polymers and Prof. V. Nazarenko for the idea and valuable discussions.