The Electro-Optical Properties of Doping Toluene in Inverted Twisted Nematic Liquid Crystals
Yen-Te Chiang1*, Tsu-Ruey Chou2, Szu-Hua Chen2, Chih-Yu Chao1,2
1Graduate Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
2Department of Physics, National Taiwan University, Taipei, Taiwan
* presenting author:Yen-Te Chiang,
In recent years, due to the flourishing growth of the mobile devices industry, the development of liquid crystal display (LCD) has greatly extended. Many kinds of liquid crystal (LC) driving modes have been improved to meet the market requirements. The conventional twisted nematic (TN) LCD with positive dielectric anisotropy LC is widely used due to its high transmission and low power consumption. On the other hand, the vertical aligned (VA) LCD with negative dielectric anisotropy LC offers excellent dark state. To combine all these advantages, inverse twisted nematic (ITN) mode, which contains 90⁰ twisted vertical aligned structure with negative dielectric anisotropy LC, has a simple fabrication process, superior contrast ratio as VA mode, and high transmission as TN mode.
We chose toluene as dopants in ITN LC to improve its electro-optical properties. After 5 wt% toluene is doped into negative NLCs, the driving voltage is 1.1V lower and the total response time is reduced by 49% compared with the pristine NLCs. This effect is due to reason that the low viscosity of toluene (0.59 cP at 20 ⁰C) decreased the rotational viscosity of NLCs after liquid doping. Moreover, the small liquid molecules penetrated between two LC molecules, which increased the separation between them and decreased their molecular interactions, leading to smaller visco-elastic coefficient. It is the first time to use liquids as dopants in negative NLCs, especially in ITN system. Our results demonstrate a simple method to optimize the electro-optical properties of ITN system and show the potential to apply this technique to other LC devices.

Keywords: liquid crystals, display, toluene