Studies of the liquid crystal surface anchoring potential using Grandjean–Cano wedge

ABSTRACT

We extend further the theoretical and experimental studies of the actual surface anchoring potential restoration by polarisation microscope technique and using micro-images in a wedge-shaped cell with weak surface anchoring forces filled by a chiral nematic liquid crystal (in Grandjean–Cano (GC) Wedge). To realize the theoretically predicted options of observation of large director deviation angles from the easy axes, the experimental studies of director distribution in GC zones were performed for differing easy axes orientations at the wedge surfaces in white light. A weak surface anchoring at one wedge surface was obtained by a photo-alignment technique. A strong surface anchoring at the second wedge surface was obtained by a rubbing. There were observed for the first time jump-less walls (without jumps of the director orientation) between neighbouring GC zones and jumps in colour in the Newton’s rings (lines) at the positions of the walls between GC zones. Qualitative explanations of the both phenomena are presented and an expression for the jump in colour value in the Newton’s rings (lines) at the positions of the walls between GC zones is presented. Some experimentally found by the polarisation microscope and by the microphoto technique images demonstrate jump-less walls between the first GC zones. To ensure optimal parameters of the further experiments on the actual surface anchoring potential restoration, theoretical calculations of the director distribution in individual GC zones were performed for various model surface anchoring potentials. It was found that especially promising for description of the experimentally found director distribution looks the modified D-potential. As a result of the present studies, the ways to enlarge (compared to the previous studies) angular range of the actual surface anchoring potential restoration were proposed.

Graphical Abstract

KEYWORDS:

• Grandjean–Cano wedge
• surface anchoring potential restoration
• polarisation microscope technique
• photo alignment

Acknowledgements

The work was supported by the RFBR grants 16-02-0295_a, 16-02-0679_a. The authors are grateful to S.S. Harlamov for the help in optical measurements.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Russian Foundation for Basic Research [16-02-0679_a,16-02-0295_a].