13C NMR investigations of molecular order of rod-like,bent-core,and thiophene mesogens

In this review, methods to obtain the orientational order of topologically variant molecular mesogens using by one- and two-dimensional (2D) solid-state ¹³C nuclear magnetic resonance (NMR) spectroscopy are described. Besides ¹³C chemical shifts, the ¹³C─¹H dipolar couplings measured from 2D-separated local field (SLF) technique are used for computing the order parameters of a variety of mesogens. The investigated molecules are composed of a variable number of rings in the core, that is, core ranging from simply one ring to five rings. Among the mesogens investigated, a special focus has been placed on mesogens with thiophene rings, which are gaining popularity as liquid crystalline organic semiconductors. The replacement of a phenyl ring by thiophene in the core has a dramatic influence on molecular topology, as observed from the measured order parameters. The review highlights the advantages of the 2D SLF method for understanding the local dynamics and for mapping the topology of mesogens through the measured order parameters. SLF NMR studies of as many as 24 molecular mesogens that vary in terms of the molecular structure as well as topology are covered in the review. Order parameters of the rings have been estimated from the ¹³C─¹H dipolar couplings in the nematic, smectic A, smectic C, and tilted hexatic phases as well as in B₁ and B₂ mesophases of various mesogens. It is anticipated that, in the years to come, the 2D SLF method would provide advanced molecular information on structurally complex mesogens that are emerging in liquid crystal science through the incessant efforts of synthetic chemists. The mini review covers the orientational order of topologically variant molecular mesogens determined by 1D and 2D solid-state ¹³C NMR spectroscopy. Accordingly, rod-like, bent-core, and thiophene mesogens were subjected to 2D SLF measurements to get the order parameters from which the topology was established. The replacement of phenyl ring by thiophene and its influence on order parameters as well as on molecular topology is also discussed.     

缩聚合成聚芳酯和聚酯－聚醚弹性体的微相复合物

通过原位直接缩聚反应，制备了刚性棒状聚对羟基苯甲酸酯（ＰＨＢ）和聚对苯二甲酸丁二醇酯－聚四亚甲基醚多嵌段共聚物（ＰＢＴ－ＰＴＭＧ）的微相复合物．复合物可溶于氯仿等溶剂，可以浇铸成膜．本文研究了ＰＨＢ含量和聚合过程中，基体聚合物溶液浓度对微相复合物形态以及力学性能影响．同共混法相比，原位缩聚法可得到分散更均匀，力学性能更优良的微相复合物．     

Controllable Preparation of Nanosized LiMnPO4/C with Rod-Like Morphology by Hydrothermal Method with Excellent Electrochemical Performance

The nanosized rod-like LiMnPO₄/C cathode materials have successfully in situ synthesized on the surface of flaky structure MnPO₄ · H₂O self-sacrificing template by the hydrothermal method. The crystal microstructure, micro shape, and electrochemical parameters of LiMnPO₄/C are comprehensively studied by XRD, SEM, TEM, and electrochemical measurement methods. The physical and chemical properties analysis confirms that the vinyl acetate solution (VAc-H₂O) with a proper molar ratio is beneficial to generate orthorhombic olivine structure LiMnPO₄ with microporous structure and nanorod-shaped morphology. The electrochemical measurement results indicate that LMP-X1-AA sample delivers an initial discharge capacity of 148.1 mAh g⁻¹ at 0.05 C, the capacity retention rate still maintains at 89.2% after 200 cycles. As the discharge rate increases to 1 C, the discharge capacity still remains at 133.4 mAh g⁻¹. The results indicate that the synergistic effect of nanosized rod-like morphology and conductive carbon coating is beneficial to improving the lithium ions diffusivity and electrochemical properties of LiMnPO₄ materials.     

Brownian dynamics simulations with spin Brownian motion on the negative magneto-rheological effect of a rod-like hematite particle suspension

We have investigated the behaviour of a suspension of magnetic rod-like hematite particles in a simple shear flow with the addition of an applied magnetic field. A significant feature of the present hematite particle suspension is the fact that the magnetic moment of the hematite particle lies normal to the particle-axis direction. From simulations, we have attempted to clarify the dependence of the negative magneto-rheological effect on the particle aggregation and orientational distribution of particles. The present Brownian dynamics method has a significant advantage in that it takes into account the spin rotational Brownian motion about the particle axis in addition to the ordinary translational and rotational Brownian motion. The net viscosity is decomposed into three components and discussed at a deeper level and in detail: these three viscosity components arise from (1) the torque due to the magnetic particle–field interaction, (2) the torque and (3) the force due to the interaction between particles. It is found that a slight change in the orientational distribution has a significant influence on the negative magneto-rheological effect. In a relatively dense suspension, the viscosity components arising from an applied magnetic field and the interaction between particles come to change rapidly for a certain strength of the magnetic particle–particle interaction, which is due to the onset of the formation of raft-like clusters.     

Axial X-ray scattering on high-performance polymeric fibers

High-temperature polymers were spum from liquid-crystalline solutions into fibers of superior thermal stability and mechanical properties. Fibers of two extended-chain polymers poly(p-phenyleneterephthalamide), PPTA, and poly-2,5-benzoxazole, ABPBO, as well as a rod-like polymer poly(p-phenylenebenzobisoxazole), PBO, were examined by axial x-ray scattering. Both wide-angle scattering and small-angle scattering were performed with CuKα radiation aiming along the fiber axis (c-axis) for structural information on the a-b lattice plane. In addition to previously reported lattice structure, the PPTA fibers (Kevlar® 29, 49, and 149) showed strong [004] and a [022] reflections suggesting that segments of the PPTA molecules were transverse to the fiber axis. This unique fiber structure is more prominent and the void content is less for the PPTA fibers with higher tensile modulus, (i.e., Kevlar® 149 > Kevlar® 49 > Kevlar® 29). Similar measurements on thermally annealed ABPBO and PBO fibers showed no [00l], [h0l], or [0kl] reflection indicative of a truly uniaxial molecular orientation. Evidence of microfibrillar order was discovered for the Kevlar® fibers and the ABPBO fiber. Results of conventional x-ray scattering on these fibers were compared and reconciled. © 1994 John Wiley & Sons, Inc.     

The motion of rigid rod-like particles suspended in non-homogeneous flow fields

Equations are written for the velocities of rotation and translation of rigid rod-like particles suspended in arbitrary Stokes flows. These make use of the first approximation from slender body theory for the evaluation of drag forces parallel and transverse to the particle axis, and neglect couples induced by shear stress at the particle surface. They are therefore asymptotically valid as the particle axis ratio becomes large. Simple forms of the equations, applying in constant viscosity flows, are solved, where possible analytically and otherwise numerically, and results obtained for particle motion in planar Poiseuille and sink flows. These are discussed and displayed in terms of appropriate dimensionless groups in a comprehensive set of plots, that can conveniently be used to provide information on translational and rotational velocities, and orientation and displacement as a function of time, including particle slip along and across streamlines, for a wide range of cases. In this way the effects of non-homogeneity in the flow fields are quantified.     

棒状分子聚合物溶液的微宏观数值模拟

利用微宏观耦合方法模拟了棒状分子聚合物溶液在平板Couette流动中的复杂流变行为,其中微宏观模型通过非均匀Doi理论来描述.数值模拟中,应用有限体积方法耦合求解了介观尺度上的Smoluchowski方程和宏观尺度上的流场守恒方程.数值结果不仅得到了若干种典型的流动类型,而且还预测了另外两种新的复合瑕疵结构.数值试验表明：棒状分子聚合物的流变结构主要依赖于De数、分子相对尺度以及溶液浓度常数的取值;并且De数对分子指向矢的翻滚周期、随流取向角等微观特性也均有明显影响. 关键词： 棒状分子 聚合物溶液 微宏观模拟     

On aggregate structures in a rod-like haematite particle suspension by means of Brownian dynamics simulations

We have investigated aggregation phenomena in a suspension composed of rod-like haematite particles by means of Brownian dynamics simulations. The magnetic moment of the haematite particles lies normal to the particle axis direction and therefore the present Brownian dynamics method takes into account the spin rotational Brownian motion about the particle axis. We have investigated the influence of the magnetic particle–field and particle–particle interactions, the shear rate and the volumetric fraction of particles on the particle aggregation phenomena. Snapshots of aggregate structures are used for a qualitative discussion and the cluster size distribution, radial distribution function and the orientational correlation functions of the direction of particle axis and magnetic moment are the focus for a quantitative discussion. The significant formation of raft-like clusters is found to occur at a magnetic particle–particle interaction strength much larger than that required for a magnetic spherical particle suspension. This is because the rotational Brownian motion has a significant influence on the formation of clusters in a suspension of rod-like particles with a large aspect ratio. An applied magnetic field enhances the formation of raft-like clusters. A shear flow does not have a significant influence on the internal structure of the clusters, but influences the cluster size distribution of the raft-like clusters.     

The crystalline molecular complex between cationic surfactant and some additive substances: Part I: complex formation with phenol derivative as additives

It was established that many crystalline molecular complexes composed of cationic surfactants such as CTAB and several phenolic derivatives were obtained from an appropriate concentrated solution system in which a remarkable viscoelasticity was developed. It is revealed that the molecular complexes have an unambiguous composition of 1:1 molar ratio of surfactants to phenolic additives. The molecular complexes also showed characteristic endothermicity of a degree that suggests the specimens to be single and a pure species. However, through repeated runs the thermal stability of the complexes seemed to be rather poor, as exhibited by a profile change in thermograms of DSC.     

Concentration dependences of the transport coefficients of rod-like molecules in narrow slit-shaped pores

The concentration dependences of the label transport and shear viscosity coefficients for rod-like molecules in slit-shaped pores were studied. The calculations were carried out using the lattice gas model, which describes a broad range of fluid concentrations (from the gaseous to the liquid state) and temperatures (including the critical region). In the calculation of the local distributions of mixture components in the equilibrium states, lateral interactions were taken into account. The translational and rotational motions of molecules were described in terms of the transition state theory for nonideal reaction systems, which took into account the influence of neighboring molecules on the height of the activation barrier. The model equations reflect the pronounced anisotropy of the distribution of system components along the normal to the pore wall surface and ordering effects of molecules along various directions. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1485–1494, September, 2006.