Au纳米颗粒对向列相液晶取向性能的影响

Influence of Au nanoparticles on the orientation of nematic liquid crystals

液晶分子的初始排列在液晶显示器中起着关键的作用。纳米粒子掺杂到液晶体系可扰乱液晶分子的排列,从而改变液晶的自组装特性,进而影响液晶的各项性能。将制备的Au八面体纳米颗粒掺杂到向列相液晶4-氰基-4′-正戊基联苯(5CB)中,灌入液晶盒后,通过使用偏光显微镜对液晶盒的观察发现,掺杂的八面体Au纳米颗粒诱导5CB液晶分子发生了垂直取向,而球形Au纳米颗粒不能诱导液晶分子垂直取向。这归因于八面体Au纳米颗粒的表面能比较小,液晶分子间的作用力比较大,使液晶分子易于垂直取向。随着O-Au NPs的浓度增大,液晶分子的取向效果先变好又逐渐变差。这是因为O-Au NPs的浓度越高,可诱导越多的液晶分子垂直取向排列,但随着纳米粒子浓度的增加,纳米粒子团聚,减少了与液晶分子的作用,使取向效果变差。动态过程实验显示,0.1%的八面体金纳米颗粒可诱导向列相液晶5CB在2 min内快速完成垂直取向,表明O-Au NPs具有优异的诱导5CB取向的动态效果。

The initial alignment of liquid crystal molecules plays a key role in LCD and has a great influence on its display performance.Doping nano-particles into liquid crystal system disturbs the arrangement of liquid crystal molecules,which changes the self-assembly characteristics and various properties of liquid crystal.The prepared Au octahedral nanoparticles were doped into nematic liquid crystal 4-cyano-4′-n-pentyl biphenyl(5 CB)and the mixture was poured into the liquid crystal cell.The vertical orientation was observed by polarizing microscope in the 5 CB doped with Au octahedral nanoparticles(O-Au NPs)but not observed in that doped with Au spherical nanoparticles(S-Au NPs).This is attributed to the fact that the surface energy of octahedral Au nanoparticles is relatively small and the interaction force among liquid crystal molecules is relatively large,which makes the liquid crystal molecules easy to orient vertically.With the concentration of O-Au NPs increasing,the orientation of liquid crystal molecules was more and more better in first then became worse later.This is because higher concentration of O-Au NPs leads to orientation of more liquid crystal molecules.With further increase of concentration of O-Au NPs,aggregation of nanoparticles occurred,reducing the interaction between O-Au NPs and liquid crystal molecules resulting in worse orientation.Dynamic experiments show that 0.1%O-Au NPs leaded to completely orientation of 5 CB in 2 min,which indicates that O-Au NPs is excellent to lead to orientation.