Stablizization And Performance Switching Of Liquid Cyrstal Blue Phase Based On Polyoxometalate-Based Organic-Inorganic Hybrids

Blue Phase liquid crystals (BPLCs), whose crystal lattice parameters can be easily influenced under conditions, possess a promising prospect in the fields of quick response electro-optic devices and tunable photonic crystals et al because of its rapid responsibility to external field, unique self-assembly properties and wonderful electro-optical properties. Unfortunately, BPs usually appear in an extremely narrow temperature range, besides its electro-optical properties can hardly satisfy practical application. In this study, we firstly use polyoxometalate (POM) organic-inorganic hybrids for stabilization and optical switching of BPs.Firstly, we develop two novel polyoxometalate (POM) organic-inorganic hybrids with covalently grafted different amount of azobenzene mesogenic moieties, and study the effect of BPLCs temperature ranges by doping them into host LCs. It comes out that the stabilization effect is different for bent-like POM hybrid 1 with two azobenzene groups and dendritic-like POM hybrid 2 with for azobenzene groups. Herein, POM hybrid 1 could help to stabilize BP I, in which the widest BP I temperature ranges is 20.5?; While POM hybrid 2 is found to be greatly effective for the stabilization of BP II, wherein the widest BP II temperature could reach 8.1?. Then, we chose the LC sample doped with POM hybrid 2 to explore the changes of optical properties of BP? based on isomerization of azobenzene groups under UV-visble light, the result shows that there is about 80 nm red-shift in Bragg reflection wavelength of BP II. Additionally, we explain the related stabilization and optical tuning mechanisms in term of molecular structures and elastic properties.Secondly, we fabricate polymerizable POM-based hybrid molecule containing with acrylate end groups. Then we study the stabilization of BPLCs doped with unpolymerizable precursor, we found that when the doping amount is 1.0 wt%, the BP temperature can be broadened to 17.4?. Moreover, we prepare polymer stabilized BPLCs by UV light irradiation after blending the polymerizable POM-based hybrid molecule,651 (photoinitiator) and C6M (crosslinker) with host LCs. The polymernetwork can remarkably stabilize and broaden BPs, which is due to the reduced free energy of the system produced by the polymernetwork filling with the disclination cores between the double-twisted cylinders (DTC). What's more, we chose the best ratio of the POM polymerizible BPLCs for further study of electro-optical responsive properties based on Kerr effect. Compared with systems without POM-based dopants, the corresponding switching voltage decreased in POM-based polymer stabilized BPLCs, we think it may be induced by the low surface energy in the BP-LC system.In conclusion, the POM-based organic-inorganic hybrids play important roles in stabilizing and optical switching of BPs. These results provide a new pathway for the optimization of BP in terms of molecular structure design.