在电场和磁场下手性侧链丙烯酸酯液晶聚合物的行为

在电场和磁场下手性侧链丙烯酸酯液晶聚合物的行为江雪平金顺子漆宗能张树范（中国科学院化学研究所北京１０００８０）关键词手性侧链丙烯酸酯液晶聚合物，红外二向色性，液晶分子排列含有手性液晶基团的聚合物，分子中含有不对称碳原子，在一定条件下使液晶聚合物...     

Structural Refinement of Carbimazole by NMR Crystallography

The characterization of the three-dimensional structure of solids is of major importance, especially in the pharmaceutical field. In the present work, NMR crystallography methods are applied with the aim to refine the crystal structure of carbimazole, an active pharmaceutical ingredient used for the treatment of hyperthyroidism and Grave’s disease. Starting from previously reported X-ray diffraction data, two refined structures were obtained by geometry optimization methods. Experimental ¹H and ¹³C isotropic chemical shift measured by the suitable ¹H and ¹³C high-resolution solid state NMR techniques were compared with DFT-GIPAW calculated values, allowing the quality of the obtained structure to be experimentally checked. The refined structure was further validated through the analysis of ¹H-¹H and ¹H-¹³C 2D NMR correlation experiments. The final structure differs from that previously obtained from X-ray diffraction data mostly for the position of hydrogen atoms.     

Enhanced photochemical‐shift of reflection band from an inverse opal film based on larger birefringent polymer liquid crystals: Effect of tolane group on the photochemical shift behavior

Photo‐chemically tunable photonic band gap materials are prepared by infiltration of liquid crystal polymers having azobenzene groups into voids of SiO₂ inverse opal films. Linearly polarized (LP) light irradiation results in transformation from a random to an anisotropic molecular orientation of azobenzene side chains in the voids of the SiO₂ inverse opal film, leading to the reversible and stable shift of the reflection peak to longer wavelength more than 15 nm. To improve switching properties, we use copolymers of azobenzene monomer and tolane monomer, which have higher birefringence, as infiltration materials into the voids. The azobenzene‐tolane copolymers are found to show higher birefringence than azobenzene homopolymers by the LP light irradiation at higher temperature. Consequently, the reflection band of the SiO₂ inverse opal film infiltrated with the azobenzene‐tolane copolymer can be shifted to longer wavelength region more than 55 nm by the irradiation of LP light. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1981–1990, 2009     

Structure and thermal properties of natural colored cottons and bombax cotton

Chemical compositions, crystalline structures and thermal properties of bombax cotton and natural colored cottons including laurel green, bottle green and brown cotton were investigated by chemical analysis, SEM, IR spectra and X-ray diffraction. The results showed that the crystallinity and crystallite sizes of laurel green cotton were lower than those of bottle green cotton because of the excess content of suberin in the former. The crystallinity of brown cotton was similar to that of white cotton, and bombax cotton had the lowest crystallinity but its crystallite orientation was the highest. Thermal property of bottle green cotton was the most stable, whose decomposition temperature was higher of 30°C than that of common white cotton because of its higher lignin content, and bombax cotton had the lowest thermal degradation temperature. But bottle green cotton reached the highest decomposition speed and made decomposition finish within a very short time, and bombax cotton was just the reverse.     

Synthesis and optoelectronic properties of liquid‐crystalline copolymers based on fluorene and triphenylamine‐containing oligo(p‐phenylenevinylene) derivatives for white light emission

A series of novel liquid‐crystalline copolymers based on fluorene and triphenylamine‐containing oligo(p‐phenylenevinylene) derivatives have been synthesized according to the Suzuki polymerization method. The structures, optical and electrochemical properties of the copolymers were characterized by ¹H NMR, ¹³C NMR, GPC, UV–vis, photoluminescence (PL) spectroscopy, and cyclic voltammetry (CV), respectively. The thermotropic phase behavior of the copolymers was investigated by using differential scanning calorimetry (DSC) and polarized optical microscope (POM). All of the copolymers exhibit thermally liquid crystalline properties and represent the characteristic Schlieren textures in a wide temperature range. The effects of the concentrations and chain length of the oligo(phenylenevinylene) units on the thermal properties, liquid crystalline, photo‐ and electroluminescent properties of the copolymers have been investigated in details. Among the copolymers‐based devices with a configuration of ITO/PEDOT:PSS/polymers/Ca/Al, the device based on PF‐LOPV05 exhibits the lowest turn‐on voltage of 3 V and the maximum brightness of 210 cd/m² at 8.3 V. A single layer device based on the blend of PF/PF‐LOPV05 emits white electroluminescence with CIE coordinates of (0.30, 0.35) at 8 V. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3296–3308, 2009     

A novel type of optically active helical liquid crystalline polymers: Synthesis and characterization of poly(p‐phenylene)s containing terphenyl mesogen with different terminal groups

Series of poly(p‐phenylene)s (PPPs) containing terphenyl mesogenic pendants with cyano and methoxy terminal groups by flexible ? COO(CH₂)₆O? bridge [ P(CN) and P(OCH₃) ] are synthesized through Yamamoto polycondensation with Ni‐based complex catalysts. The effects of the structural variation on their properties, especially their mesomorphism, ultraviolet–visible (UV), and photoluminescence behaviors, are studied. All of the polymers are stable, losing little of their weights when heated to ≥340 °C. The polymers show good solubility and can be dissolved in common solvents. P(CN) with cyano terminal group shows enantiotropic SmA_d phase with bilayer packing arrangement, while P(OCH₃) with methoxy terminal group readily forms nematic and SmA_d phase when heated and cooled. Photoexcitation of their solutions induces strong blue light emission. Compared with P(OCH₃) , the light‐emitting bands of polymer P(CN) is slightly redshifted to 428 nm and the emission intensity of P(CN) is much stronger, due to the existence of donor–acceptor pairs. More interestingly, both of the polymers exhibit obvious Cotton effect on the CD spectra, resulting from the predominant screw sense of the backbone. This indicates that the bulky mesogenic pendant orientating around the backbone will force the main chain with helical conformation in the long region due to steric crowdedness. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4723–4735, 2009     

Spinodal decomposition and nematic coarsening in a rigid-rod solution

The dynamics of a solution of rodlike liquid-crystalline molecules are simulated for the related problems of isotropic–nematic spinodal decomposition and the coarsening of misaligned nematic grains. The Doi diffusion equation for the rod distribution function is coupled with the full Onsager intermolecular potential, discretized by the finite-element method, and integrated forward in time by using a parallel, semi-implicit scheme. The Onsager potential models rod interaction on the scale of a single rod length in order to resolve accurately defects and interfaces in structure. Simulation results show the effects of rotational and translational diffusivity ratios on the mechanisms for alignment and phase separation in spinodal decomposition. As rotational motion is restricted, individual grains become more aligned prior to coalescence events. When rods are restricted to diffusive motion along their axis, the spinodal decomposition process is arrested, and the system will reach a pseudo-steady state featuring misaligned nematic grains. These results mark the first dynamic computation of the Doi diffusion equation for spinodal decomposition in nonhomogeneous rigid-rod systems. Nematic coarsening simulations show the effects of misalignment between neighboring ordered domains on the coarsening time and director field around structured interfaces. Results show that the coarsening time is dependent not only on misalignment between grain directors, but also on the tilt angle of the directors into the interface.     

Effect of crystalline lens surfaces and refractive index on image quality by model simulation analysis

The surfaces and refractive index of crystalline lens play an important role in the optical performance of human eye.On the basis of two eye models,which are widely applied at present,the effect of lens surfaces and its refractive index distribution on optical imaging is analyzed with the optical design software ZEMAX (Zemax Development Co.,San Diego,USA).The result shows that good image quality can be provided by the aspheric lens surfaces or (and) the gradient-index (GRIN) distribution.It has great potential in the design of intraocular lens (IOL).The eye models with an intraocular implantation are presented.     

Evaluation of the electron momentum density of crystalline systems from ab initio linear combination of atomic orbitals calculations

Alternative techniques are presented for the evaluation of the electron momentum density (EMD) of crystalline systems from ab initio linear combination of atomic‐orbitals calculations performed in the frame of one‐electron self‐consistent‐field Hamiltonians. Their respective merits and drawbacks are analyzed with reference to two periodic systems with very different electronic features: the fully covalent crystalline silicon and the ionic lithium fluoride. Beyond one‐electron Hamiltonians, a post‐Hartree–Fock correction to the EMD of crystalline materials is also illustrated in the case of lithium fluoride. © 2012 Wiley Periodicals, Inc.     

Brittleness of protein crystals

A simple technique for studying the brittleness of small crystals is reported. The limits of fracture toughness of tetragonal hen‐egg white lysozyme crystals, oriented with their c‐axis normally to the substrate, were measured. The strong mechanics anisotropy of those crystals was confirmed. The role of the water present in the protein crystal lattice was re‐considered in seek for a more holistic understanding of the process, the idea being that the intra‐crystalline solution sustains the globular protein molecules in their native configuration. Also it is argued that this water may contribute for holding together the huge bio‐molecules in the crystal lattice (that is to act as additional “glue” in the crystal). The hypothesis is that dynamic chains of H‐bonds in the intra‐crystalline water are likely to be prolonged to connect protein‐to‐water‐to‐protein.