Research On Electro-optical Properties Of Cholesteric Liquid Crystal Based On Chiral Ionic

Cholesteric liquid crystals (CLCs) possess Bragg reflection characteristic. The reflection bandwidth of traditional CLCs is less than 150 nm owing to limits of single pitch and birefringence, which is insufficient in reflective display such us multi-functional color films, optical storage, and electronic reading. Therefore, wide applications will be obtained by studying the wide reflection bandwidth of cholesteric liquid crystals. Reseacher proposed to prepare wide reflection bandwidth cholesteric liquid crystals by introducing a non-uniform pitch distribution or a pitch gradient in the CLCs based on heat, light, and electricity, which obtained a lot of excellent work. However, the reflection bandwidth of above study cannot be tuned. Although recently many papers report methods to tune the reflection bandwidth of CLCs by heat or light, a few of defect still exist such as rough tuning process, heat-labile, high electric field, or simple single direction adjustment.On account of these points, a new scheme to prepare cholesteric liquid crystal with electrically controllable reflection bandwidths based on ionic polymer networks was proposed based on electric field tuning. Firstly, chiral ionic was introduced to CLCs to prepare wide reflection bandwidth device. The mechanism of ions movement induced by electric field and the corresponding reflecting property of CLC were studied, which is a steppingstone to further subsequent studies. Secondly, an new chiral ionic monomer was prepared and was added to suitable CLCs which were chosen according to consistency in composite. Secondly, the mechanism of forming polymer network and the network control technology were studied. Finally, polymer stabilized cholesteric texture with electrically tunable wide reflection bandwidth was prepared with a range from 373 nm to 153 nm by a serious of electric field scheme. Meanwhile, the reflection bandwidth can be increased or decreased with low electric field. The studied work has great potential for practical application such as colorful electronic papers, traffic signs, wearable devices, and intelligent windows.A multi-stable and electrically switchable cholesteric liquid crystal based on chiral ionic liquid is also studied. In the experiment, chiral ionic was introduced to CLCs with electric field to induce movement of CIL forming pitch gradient and driving the negative liquid crystal molecules into new orientation arrangement. According to above mechanism, the cholesteric liquid crystal can be switched among planar texture, focal conic texture, wide-band reflected state and fingerprint texture by applying specific electric fields, which prepares the four stable states of CLCs for the first time. The multi-stable and electrically switchable CIL doped CLC has great potential for practical application such as large billboards, traffic signs, intelligent windows, and smart sun glasses.