The electro-optical characteristics and applicability evaluation of a photo-induced vertical alignment negative-type liquid crystal/photo-curable acrylic pre-polymer mixture system mixed with chiral smectic A phase liquid crystal

Abstract

In this study, we have investigated newly synthesised chiral smectic A (SmA*) liquid crystals (LCs) with a lactic acid structure with polarised optical microscopy (POM). We started cooling from the clear point until a SmA* phase emerged as the temperature dropped to the range 55.7–88.6°C. At this point, the alignment of the LC molecules resulted in a homeotropic texture. To take advantage of this characteristic, we then mixed the SmA* LC into a negative dielectric anisotropy nematic-type liquid crystal (NLC)/photo-curable acrylic pre-polymer mixture system (the NLC mixture system) with photo-induced vertical alignment, to realise the vertical alignment effect among the NLC molecules. This multi-component LC mixture system gave rise to a special, unknown twist grain boundary AX (TGB _AX *) phase with rather broad temperature range, which maintained its helix structure even after crystallisation. In addition, we also utilised the electrical field induced molecular tilt effect (the electroclinic effect) within the SmA* LC to improve the response time of the LC device and gray-scale capability of the NLC mixture system. We further observed this multi-component LC mixture system after ultraviolet light irradiation treatment with POM, to investigate the alignment of the LC molecules, device display and electro-optical properties.

Keywords:

• liquid crystal
• homeotropic texture
• twist grain boundary
• electroclinic effect

Acknowledgements

The authors would like to thank Mr Kai-Neng Yang from Chimei Innolux Corporation for supplying the photo-curable acrylic pre-polymer and photo-initiator materials for the experiment, and for offering numerous advice and suggestions which were invaluable in facilitating the smooth completion of the experiment.