Research On Electro-optic Property Of Polymer-stabilized Blue Phase Liquid Crystal With Electric Field During Polymerization

Blue phase liquid crystal(BPLC)exists in a narrow temperature range between isotropic phase and chiral nematic phase,which consists of double twist cylinders(DTCs)and disclination lines.BPLC exhibits some attractive features,such as sub-millisecond response time,three-dimensional(3-D)self-assembled cubic structure,macro optical isotropic without electric field.The BPLC has a narrow temperature of 1~2 K.Recently,several approaches have been proposed to improve the thermal stability of BPs.Since the temperature range was broadened to more than 60 K by polymer stabilization in 2002,BPLC shows potential applications in field sequential displays,3-D photonic devices,and phase modulators.However,some issues,such as high driving voltage,weak thermal stability,hysteresis,residual birefringence,and scattering at dark state,should be solved prior to the wide application of polymer-stabilized blue phase liquid crystal(PS-BPLC).In this paper,the effect of liquid crystal host,chiral dopant,and monomers on BPLC is investigated to improve the electro-optic properties of BPLC device.The research on the composition of BPLC mixtures provides the foundation of research on improvement of BPLC materials.The effect of multiple-doping based on reactive diluent and conductive polymer is investigated.It is found that the multiple-doping can decrease the interfacial energy between the polymer network and DTCs and increase the conductivity of material system.With the optimized concentration of 0.99% NVP and 0.05% G-PANI,the Kerr constant is increased by 68% in comparison with that of PS-BPLC without doping.Meanwhile,the hysteresis,the response time,and the residual birefringence have no degradation.The stabilization process by applying electric field to the BPLCs is demonstrated to improve the contrast ratio and Kerr constant of PS-BPLC.The electric field applied during polymerization can enhance the uniformity of blue phase domain resulting in a good dark state.Meanwhile,the potential energy of the BPLC molecules can lower the anchoring energy of the polymer network,which improves the Kerr constant of PS-BPLC.The frequency effect of the electric field in polymerization process is investigated to improve the contrast ratio of PS-BPLC with large Kerr constant.With an optimized electric field,0.37 V/?m at the frequency of 500 kHz,the contrast ratio and the Kerr constant of PS-BPLC can be improved by 4.1 times and 15%,respectively,and hysteresis can be decreased by 10%,while the response time and residual birefringence will not suffer from degradation.