负折射超材料响应中心频率的液晶调控

提出开口金属环加液晶的三明治超材料结构,将优化的超材料金属环线结构单元与液晶相结合,采用外加电场调节液晶的介电系数,使该结构的负折射响应中心频率可在一定范围内较方便、反复的调整.通过模拟仿真和理论分析证明这是一个可行的结构模型.     

Nematic DNA Thermotropic Liquid Crystals with Photoresponsive Mechanical Properties

Over the last decades, water‐based lyotropic liquid crystals of nucleic acids have been extensively investigated because of their important role in biology. Alongside, solvent‐free thermotropic liquid crystals (TLCs) from DNA are gaining great interest, owing to their relevance to DNA‐inspired optoelectronic applications. Up to now, however, only the smectic phase of DNA TLCs has been reported. The development of new mesophases including nematic, hexagonal, and cubic structures for DNA TLCs remains a significant challenge, which thus limits their technological applications considerably. In this work, a new type of DNA TLC that is formed by electrostatic complexation of anionic oligonucleotides and cationic surfactants containing an azobenzene (AZO) moiety is demonstrated. DNA–AZO complexes form a stable nematic mesophase over a temperature range from ?7 to 110 °C and retain double‐stranded DNA structure at ambient temperature. Photoisomerization of the AZO moieties from the E‐ to the Z‐ form alters the stiffness of the DNA–AZO hybrid materials opening a pathway toward the development of DNA TLCs as stimuli‐responsive biomaterials.     

Molecular Dynamics Calculation of the Viscosities of Biaxial Nematic Liquid Crystals

We have evaluated the Green–Kubo relations for the viscosities of a biaxial nematic liquid crystal by performing equilibrium molecular dynamics simulations. The viscosity varies by more than two orders of magnitude depending on the orientation of the directors relative to the streamlines. The molecules consist of nine fused Gay–Berne oblates whose axes of revolution are parallel to each other and perpendicular to the line joining their centers of mass. This gives a biaxial body, the length-to-width-to-breadth ratio of which is equal to 5:1:0.4. The numerical evaluation of the Green–Kubo relations for the viscosities is facilitated by the application of a Gaussian director constraint algorithm that makes it possible to fix the directors in space. This does not only generate an inertial director-based frame but also a new equilibrium ensemble. In this ensemble the Green–Kubo relations for the viscosities are simple linear combinations of time correlation function integrals, whereas they are complicated rational functions in the conventional canonical ensemble.     

Relationship between Elastic Constants of Nematic Liquid Crystals and Molecular Pair Potential

Thenanke1asticconstantsk11,k22andk33areameasureofthefreeenergyassociatedwithlong-wavelengthdistortions0fthenematicstateinwhichthelocalpreferreddirectionofmolecularorientationvariesinspace.Theyappearinvariousc0ntextsinnu-merousapplicationsofliquidcrystalsanditisthere-foreofinteresttorelatethemwiththemolecularpairpotentialtliroughthestatisticaltheory.Poniewier-skyandStecki[1lhaveobtainedageneralexpressionfortheelasticconstalltsofnematicsintermsofthedi-rectcorrelationfunction.HereP0niewiersky-St…     

双光轴偶氮液晶分子光致异构的机理研究

双光轴偶氮液晶(biaxial nematic azo liquid crystal)具有光致异构特性、良好的稳定性和可逆性等优点,可通过结构修饰和外部电场控制进一步提高材料性能,从而降低写入激光波长,提高稳定温度和反应速度,在高密度光学存储材料中具有极大的潜在应用价值.综述了双光轴偶氮液晶分子光致异构机理的近期研究结果,分析了它对偏振光选择吸收时发生顺反循环异构的动力学过程,展示了其实际应用.     

双光轴偶氦液晶分子光致异构的机理研究

双光轴偶氮液晶（biaxial nematic azo liquid crystal）具有光致异构特性、良好的稳定性和可逆性等优点，可通过结构修饰和外部电场控制进一步提高材料性能，从而降低写入激光波长，提高稳定温度和反应速度，在高密度光学存储材料中具有极大的潜在应用价值。综述了双光轴偶氮液晶分子光致异构机理的近期研究结果，分析了它对偏振光选择吸收时发生顺反循环异构的动力学过程，展示了其实际应用。     

Statistical Calculation of the Viscous Properties of Nematic Liquid Crystals by Means of the Kinetic Equation for the Tensor Order Parameter

We carried out statistical calculation, of the viscosity coefficients of nematic liquid crystals. As the starting point of calculation, we used the expression for the tensor of viscous stresses obtained within the framework of the relaxational hydrodynamics of investigated media constructed on the basis of Zubarev's method of nonequilibrium statistical ensembles. The relaxational equation for the tensor order parameter was used to calculate the time correlation functions that determine kinetic coefficients. The results of theoretical calculations were compared with experimental data on the temperature dependence for a number of nematogens.     

Enhanced Dynamic Adhesion in Nematic Liquid Crystal Elastomers

Smart adhesives that undergo reversible detachment in response to external stimuli enable a wide range of applications in household products, medical devices, or manufacturing. Here, a new model system for the design of smart soft adhesives that dynamically respond to their environment is presented. By exploiting the effect of dynamic soft elasticity in nematic liquid crystal elastomers (LCE), the temperature‐dependent control of adhesion to a solid glass surface is demonstrated. The adhesion strength of LCE is more than double in the nematic phase, in comparison to the isotropic phase, further increasing at higher detachment rates. The static work of adhesion, related to the interfacial energy of adhesive contact, is shown to change very little within the explored temperature range. Accordingly, the observed enhanced adhesion in the nematic phase is primarily attributable to the increased internal energy dissipation during the detachment process. This adhesion effect is correlated with the inherent bulk dynamic‐mechanical response in the nematic LCE. The reported enhanced dynamic adhesion can lead to the development of a new class of stimuli‐responsive adhesives.     

Birefringence Measurement of Liquid Crystals

The cylindrical cell method for determining the refractive indices of liquid crystals is described. This method is based on the use of a cylindrical cell composed of a pair of semi-cylindrical prisms and the measurement of the incident angle dependence of transmitted light intensities. It is applied to the measurement of refractive indices of nematic and cholesteric liquid crystals.     

向列型热致液晶聚酰胺的结构表征

采用傅立叶红外光谱仪（IR）、广角X射线衍射仪（WAXD）、热台偏光显微镜（POM）及扫描电子显微镜（SEM）对所合成热致液晶聚酰胺进行了结构表征。IR谱图显示了该聚合物为半刚性结构,与所设计的分子结构相一致;WAXD曲线显示处于液晶态的聚合物在2θ=20°左右有一弥散的峰,表明该液晶聚合物为向列型液晶结构;POM观察...     

Advances in Biological Liquid Crystals

Biological liquid crystals, a rich set of soft materials with rod‐like structures widely existing in nature, possess typical lyotropic liquid crystalline phase properties both in vitro (e.g., cellulose, peptides, and protein assemblies) and in vivo (e.g., cellular lipid membrane, packed DNA in bacteria, and aligned fibroblasts). Given the ability to undergo phase transition in response to various stimuli, numerous practices are exercised to spatially arrange biological liquid crystals. Here, a fundamental understanding of interactions between rod‐shaped biological building blocks and their orientational ordering across multiple length scales is addressed. Discussions are made with regard to the dependence of physical properties of nonmotile objects on the first‐order phase transition and the coexistence of multi‐phases in passive liquid crystalline systems. This work also focuses on how the applied physical stimuli drives the reorganization of constituent passive particles for a new steady‐state alignment. A number of recent progresses in the dynamics behaviors of active liquid crystals are presented, and particular attention is given to those self‐propelled animate elements, like the formation of motile topological defects, active turbulence, correlation of orientational ordering, and cellular functions. Finally, future implications and potential applications of the biological liquid crystalline materials are discussed.