Fabrication of pseudo-pi vertical alignment mode liquid crystal devices with ultra-violet polymerisation and investigations of their electro-optical characteristics

Abstract

In this study, we applied the non-contact photo-polymerisation method in fabricating pseudo-polyimide (PI) liquid crystal (LC) devices with vertical alignment copolymer films, in the hope of solving the problems associated with traditional rubbing alignment processes. We mixed different photo-polymerisation-type acrylic monomers and negative dielectric anisotropy LC at proper weight percentages, and induced phase separation behaviour between the photo-polymerisation-type acrylic monomers and the LC molecules in the LC mixture solution through ultra-violet light irradiation, thereby forming copolymer films with vertical alignment effects. We further conducted preliminary characterisation of the alignment mechanism, photo-polymerisation, etc., of the LC molecules and investigated their interactions with alkyl acrylic monomers with different carbon chain lengths (the analogue of alkyl side chains in traditionally used vertical alignment-type PI) and electro-optical properties such as the transmittance, contrast ratio, and response time.

Keywords:

• liquid crystal
• vertical alignment
• negative dielectric anisotropy
• phase separation

Acknowledgements

The authors would like to express their gratitude to Mr. Kai-Neng Yang, from SeaEn Special Material Co. Ltd, for supplying the acrylic monomers A and B, and photoinitiator for the experiment, as well as for his advice and suggestions which helped to facilitate the smooth completion of the experiment.