Effect of doped TiO₂ nanoparticle size on the ion effect of nematic liquid crystal cell
Tsu-Ruey Chou1*, Jung Hsieh2, Wei-Ting Chen1, Chih-Yu Chao1,2
1Department of Physics, National Taiwan University, Taipei, Taiwan
2Institute of Applied Physics, National Taiwan University, Taipei, Taiwan
* presenting author:Tsu-Ruey Chou, email:trchou@phys.ntu.edu.tw
Doping nanomaterials into liquid crystals (LCs) receives great attention in recent years because of possible new characteristics such as threshold voltage reduction induced by doping silicon dioxide nanoparticles. To date, there are many kinds of nanomaterials used as nanodopants, such as conductive nanoparticles, semiconducting nanoparticles, insulating nanoparticles, and carbon-related nanoparticles. In this study, titanium dioxide (TiO₂) nanoparticles with several sizes were chosen as nanodopants in order to reduce the impurity ions in nematic LCs. Transient currents and voltage-transmittance characteristics of these LC suspensions have been measured and discussed. The experimental results showed that doping TiO₂ nanoparticles into nematic LCs leads to a reduction in the moving-ion density and the amount of reduced impurity ions is related to the size of doped TiO₂ nanoparticles. Under the same doping concentration, TiO₂ nanoparticle with smaller average particle size is more effective in trapping the impurity ions. Compared with the sample without doping nanoparticles, the transported ion concentration decreased from 13.87 C / m³ to 8.63 C / m³, 7.20 C / m³, and 6.90 C / m³ for each suspension with 30-40 nm, 10 nm, and 5 nm TiO₂ nanoparticles, respectively. In addition, the threshold voltage reduction was also observed in the LC doped with TiO₂ nanoparticles. This study suggests that the TiO₂ nanoparticle with smaller size is a better candidate as nanodopant for liquid crystal display application.

Keywords: Liquid crystals, Ion effect, Titanium dioxide