| The earliest discovery of cholesteric liquid crystals(CLCs)can be traced back to 1889,named by Friedel et al,which attracted much attention due to its unique spatial spiral structure.CLCs are similar to nematic liquid crystals and near-crystalline liquid crystals,except that they have many chiral groups in their molecular structure.In CLC,the molecules are arranged to be layers,and each layer has its specific arrangement direction.It is because of the chiral groups that a certain spatial angle is generated between the two adjacent layers,thus resulting in the spiral structure.CLCs exhibit physical properties that are not found in other materials because of their unique molecular arrangement,such as optical rotation,selective reflectance,and circularly polarized dichroism.These good properties make it widely used in various fields,such as display,information,sensing and so on.However,in general,CLCs are liquid with high molecular fluidity,poor stability and susceptibility to temperature.CLC polymer,a kind of polymer material,is made of CLC mixed with a small amount of monomer,and then synthesized by UV polymerization.It not only has all the optical properties of CLC,but also is not easily affected by temperature.Based on cholesteric liquid crystal polymers,two kinds of nonplanar structures of polymerized cholesteric liquid crystals(PCLC)were studied,which are PCLC microdisk and flexible PCLC film.The optical properties of these structures are investigated by means of platforms of lasing test and tensile test.They might be applied in many fields,such as microlaser,security identification,flexible device,intelligent device and so on.The main investigation can be divided into two parts as follows:(1)The centrifugal microfluidic chip with gradient section was prepared by wet-etching method,and then PCLC droplets prepared by glass-capillary-based microfluidics were injected into the chip.After centrifugation and UV irradiation,PCLC microdisks with controllable size were obtained.In order to investigate the influence of different methods for doping fluorescent dye on optical properties of PCLC microdisks,two kinds of microdisks were produced by using centrifugal microfluidics,which were directly doped with dye before polymerization and doped with dye after washing-out/refilling.The PCLC microdisks were studied in following aspects:the relationship between initial droplet size and microdisk size at the same centrifugal speed;laser characteristics of microdisks with different thicknesses and with various temperature;the reflective band of washing-out/refilling microdisks is measured with four stages;the dependence of lasing characteristics and temperature of PCLC microdisks after washing-out and refilling;based on PCLC microdisks with washing-out/refilling,their multi-wavelength spectra created by the unique surface texture,can be converted to be a unique barcode by calculating full width at half maximum(FWHM)of laser spectrum.(2)The PDMS substrate is treated by oxygen plasma,and the chemical bond(-Si-O-Si-)is formed by polymerized cross-linking reaction.The PCLC layer is adhered to the PDMS surface,and then flexible PCLC film is produced.In this paper,two kinds of PCLC films containing E7 and XH154T7023 were prepared,respectively.The optical properties of flexible PCLC films are studied and the possibility of surface modification of flexible PCLC films was explored.flexible PCLC films were studied in following aspects:reflection characteristics of flexible PCLC film at different tensile degrees;the influence of different thicknesses of PCLC films on tensile properties;the"vector-integral" method is used to simulate the reflective characteristics of flexible PCLC films under the conditions of tensile degree<40%;the tensile characteristics of flexible PCLC films with liquid crystal XH154T7023 after washing-out and filling with UV-curing agent NOA 61. |
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