Multistable Optical Properties Of Physical/Chemical Composite Gel System Based On Cholesteric Liquid Crystals

Cholesteric liquid crystals(CLCs)can form helical microstructures in space with self-assembled characteristics,which enable CLCs to have unique optical properties such as Bragg reflection,optical rotation and laser emission due to their unique one-dimensional chiral photonic crystal superstructures,and have been applied to liquid crystal(LC)display devices,LC lasers,smart windows and etc.However,they are easy to be affected by the electric field,magnetic field,thermal field and light,which leads to the structural changes because of the instability of the helical microstructure.By adding gelators to CLCs,the LCs can be anchored to form a gel stable state with better structural stability.LC gels can be divided into reversible physical gels and irreversible reactive mesogen monomers which can enable CLCs to be mutistable.In this thesis,we fabricated the physical/chemical composite gel system with LC physical gels and reactive mesogen monomers,then analyzed its optical properties,including the following aspects.1.A multistable LC physical gel layer was fabricated by doping thermal responsive gelators 12-hydroxystearic acid(HSA)into CLCs,and the appropriate doping concentration of HSA was determined by comparing the reflectivity of CLCs with different HSA concentrations and the structural stability under the electric field.Further more,the reflectance of HSA-doped CLCs,at different cooling rates,was compared and the preparation process of LC physical gels was optimized.Finally,LC molecules can be influenced by electric field at elevated temperature and stabilized by cooling down temperature.2.The polymer stabilized cholesteric liquid crystal(PSCLC)was fabricated by doping the reactive mesogen monomers into the CLCs under UV exposure.We can wash a LC polymer to get skeleton,which used alcohol to soak out CLCs/unpolymerized monomers in PSCLC.Finally,nematic liquid crystals(NLC)are filled into the polymer network,simultaneously the reflection band reappeared after refilling NLC.3.By the wash-out/refill process,the LC physical gel doped with HSA was then filled into the polymer network of PSCLC,and a double-layer LC composite gel system with different structures was realized in a specific cell.The specific manipulation in the phase stable of LC physical gel layer is realized in the composite system taking advantage of the different thermal stability characteristics of different gels.