Ion beam induced liquid crystal alignment properties of 4-alkylphenoxymethyl-substituted polystyrenes

Abstract

The pretilt angles of liquid crystals (LCs) can be controlled over the range 0° to 90° using ion beam treated 4-alkylphenoxymethyl-substituted polystyrene films as alignment layers, where the alkyl group is –(CH₂) _n H (n = 1, 2 or 4), by changing the ion beam irradiation time, incidence angle and energy. In general, LC cells made using a polymer film with a longer irradiation time, higher irradiation incidence angle with respect to the planar direction and higher irradiation energy exhibited lower pretilt angles relative to the planar direction. Furthermore, the LC cells produced using polymer films containing longer alkyl groups and a higher molar content of 4-alkylphenoxymethyl side groups exhibited greater pretilt angles under similar irradiation conditions. The LC alignment behaviour demonstrated good correlation with the wettability of the polymer films, due to fragmentation of the side groups on the polymer surfaces during ion beam irradiation. The electro-optical characteristics of the LC cells formed using these polymer films were similar to those produced using rubbed polyimide films, which are the LC alignment layers most commonly encountered.

Keywords:

• liquid crystal
• alignment
• ion beam
• polystyrene

Acknowledgements

We gratefully acknowledge the financial support provided by the Engineering Research Institute at Seoul National University; a government-funded MOEHRD Korea Research Foundation Grant (Basic Research Promotion Fund; Grant No. KRF-2008-314-D00112); and a Korea Science and Engineering Foundation (KOSEF) grant, also funded by the Korean government (Grant No. R2009-007711). Financial assistance has also been received from Soongsil University and from Samsung Electronics Co. Ltd.

We are grateful to our colleague Eun-Ho Sohn at Seoul National University for a number of helpful discussions and for assistance with the manuscript.