Synthesis and properties of photochromic cholesteric liquid crystalline polysiloxane containing chiral mesogens and azobenzene photochromic groups

A series of novel thermotropic side‐chain liquid crystalline polymers(P₀–P₁₂) were synthesized by grafting copolymerization of mesogenic monomer cholesteryl undecylenate (M1) and photochromic monomer 4‐allyoxy‐4′‐nitroazobenzene (M2) on polymethylhydrosiloxane. The chemical structures of polymers were characterized by infrared (IR) and ultraviolet (UV) spectroscopy. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to measure the thermal properties of those polymers, and the mesogenic properties were characterized by polarized optical micrograph, DSC, wide‐angle X‐ray diffraction and small‐angle X‐ray scattering. The glass transition temperatures (T_gs) of the polymers increased from P₀ to P₄ and decreased from P₅ to P₁₂. The clearing point temperatures (T_is) of the polymers P₁–P₁₂ were lower than that of P₀, but increased from P₁ to P₄ and decreased from P₅ to P₁₂. They showed thermotropic liquid crystalline properties in a broad mesogenic region at temperatures >100°C. The polymers P₀–P₈ exhibited a cholesteric mesophase with oily streaks and lined texture, and polymers P₉–P₁₂ showed a chiral smectic mesogenic phase with a layered texture. All of the polymers were thermally stable to ～ 320°C. The UV‐induced trans–cis photoisomerization was investigated for the azo monomer and polymers P₈ and P₁₂. The solution of the azo monomer and liquid crystalline polymers P₈ and P₁₂ can undergo photoisomerization, and the environments of the azo group were responsible for the aforementioned photochemical process. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 2155–2162, 2002     

胆甾相液晶双轴特性的计算

采用自洽模拟方法计算了胆甾相液晶双轴序参数随温度和分子手征作用强度的变化,并与实验进行了比较。结果表明,双轴特性与液晶物质和温度有关,但主要产生于胆甾相液晶的螺旋结构、分子的手征特性和取向的有序性     

胆甾相液晶的制备及其显色示温混合液晶的配制

使用高效酯化催化剂法制备了两种烯酸胆甾醇酯样品。该法具有操作简便、毒性低、产率高及后处理简单的显著优点。采用元素分析、红外光谱、DSC和热台偏光显微镜等方法对样品的化学结构和液晶性能进行了表征。将合成的两种烯酸液晶样品与其它胆甾型液晶进行了混合液晶的调配与显色示温试验。结果表明,烯酸胆甾醇酯液晶作为混合液晶组分,不仅具有珍珠般的光泽,而且颜色变化灵敏,色彩艳丽。红、绿、蓝三种颜色的变色温度在室温附近,且变色温度范围较窄,在23℃之间,每种颜色变化约为1℃。     

Controlling the Phase Behavior and Reflection of Main-Chain Cholesteric Oligomers Using a Smectic Monomer

Cholesteric liquid crystals (CLCs) are a significant class of temperature-responsive photonic materials that have the ability to selectively reflect light of a specific wavelength. However, the fabrication of main-chain CLC oligomers with dramatic reflection band variation upon varying the temperatures remains a challenge. Here, a feasible method for improving and controlling the responsiveness of main-chain cholesteric liquid crystal oligomers by the incorporation of a smectic monomer is reported. The smectic monomer strengthens the smectic character of the oligomers and enhances the magnitude of the change of the pitch as a function of temperature upon approaching the cholesteric–smectic phase transition temperature. The central wavelength of the reflection band can be easily modified by mixing in an additional chiral dopant. This promising method will open the door to the preparation of temperature-responsive photonic devices with excellent responsiveness.     

纤维素纳米晶体彩色膜制备进展

纤维素纳米晶体(CNC)是由天然高分子材料纤维素制备的一种新型材料。利用CNC胶体悬浮液的自组装性能形成的胆甾型液晶相,通过超声并添加相应电解质等方法,可以制成具有良好光学性能的CNC彩色膜。本文介绍了CNC的制备方法,CNC彩色膜的形成原理、制备方法及表征手段,在总结前人工作的基础上,分析了CNC彩色膜应用受到的限制,并提出了CNC彩色膜未来的发展方向。     

Color gamut of cholesteric liquid-crystal films and flakes by standard colorimetry

Despite angle dependence and polarization selectivity, the color of cholesteric liquid-crystal (CLC) polysiloxane films can be quantified by standard colorimetry. A new fractured form of the film called “flakes” makes it possible to use the Center of Gravity Color Mixing Principle to predict the chromaticity of CLC color mixtures. A complete color gamut can be produced by layering CLC films, mixing CLCs physico-chemically, and mixing CLC flakes. © 1998 John Wiley & Sons, Inc. Col Res Appl, 23, 210–220, 1998     

Studies on the effect of substitution degree on the liquid crystalline behavior of cyanoethyl chitosan

An alkali–chitosan method was employed to prepare cyanoethyl chitosan (CNCS) with different degrees of substitution (DS) from chitosan by controlling the reaction time. The effect of the DS (from 0.36 to 1.21) on the liquid crystalline behaviors of CNCS was investigated. The critical concentration and texture of CNCS liquid crystalline in dichloroacetic acid and formic acid showed no obvious dependence on the DS. However, increase of the DS could enhance the birefringence of liquid crystalline solutions under a polarized microscope, which implied improved liquid crystallinity. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 76: 2057–2061, 2000     

含羧酸与胆甾基元的硅氧烷类聚合物的液晶性能

合成了液晶单体4-烯丙氧基苯甲酸胆甾醇酯(Mch)和单体4-十一烯酸苯甲酸(Mc),通过硅氢加成反应得到了系列侧链液晶聚合物P0~P5。通过差示扫描量热(DSC)、偏光显微镜(POM)、旋光分析等手段对聚合物的液晶性能和相行为进行了表征,结果表明,含羧基的单体Mc(P1~P5)与不含羧基的单体Mc(P0)的聚合物相比,玻璃化转变温度(Tg)、比旋光度和清亮点(Ti)均明显降低,但是没有改变原聚合物的胆甾相类型;随Mc在液晶聚合物中摩尔百分数的增加,Tg继续降低,而Ti升高。Mc的引入拓宽了液晶聚合物的介晶区间。     

Bio-Inspired Cholesteric Phase Cellulose Composite with Thermochromic and Circularly Polarized Structural Color for Multilevel Encryption

The escalating need for enhanced cryptographic security necessitates the development of advanced materials designed for the secure storage and transmission of information. Drawing inspiration from the unique color-altering and polarizing capabilities of beetles, this work develops a transparent, thermochromic, and circularly polarized cholesteric phase cellulose composite (CPCC). This is achieved by integrating self-assembled hydroxypropyl cellulose with cholesteric liquid crystal (CLC) structure in tandem with a crosslinked poly(N-isopropyl acrylamide) (PNIPAM) network. The crosslinking density impacts the response degree of thermochromism, which can be regulated by modifying the UV exposure time during PNIPAM production. The CLC structure in CPCC uniquely results in reflected right circularly polarized light. When coupled with waveplates, this mechanism inverts the rotation direction of the reflected light, creating orthogonal structural colors of different brightness levels under left and right circularly polarized light. The excellent transparency of CPCC facilitates seamless integration with the environment, offering optimal camouflage. Sophisticated techniques, such as color coding and Morse coding, can further be incorporated within the CPCC to increase encryption security and the complexity of decryption. Collectively, the CPCC's transparency, thermochromism, and chirality present significant potential in the design and development of materials for high-security information encryption, contributing valuable insights to the field.