Morphology and physical properties of a liquid–crystalline main-chain polymer with flexible side chains

A molecular laminate model is used to explain the properties of unoriented and oriented films of poly(p-phenylene-2,5-didodecyloxyterephthalate) cast from solution. In oriented films the two different crystal modifications, A and B, give rise to room temperature tensile moduli of 15 and 30 GPa respectively. The packing (in clusters) of the side chains in modification A, leading to a glass–like transition in the side-chain regions around ?40°C, is largely responsible for this difference. Oriented films of modification A and B have coefficients of thermal expansion of +0.3×10^?5 and ?1× 10^?5 K^?1 respectively. It is concluded that the properties of this class of polymers can be adjusted in a systematic way.     

On cyclically orientable graphs

Graph G is called cyclically orientable (CO) if it admits an orientation in which every simple chordless cycle is cyclically oriented. This family of graphs was introduced by Barot et al. [Cluster algebras of finite type and positive symmetrizable matrices, J. London Math. Soc. (3) 73 (2006) 545-564]. The authors obtained several nice characterizations of CO-graphs, being motivated primarily by their applications in cluster algebras. Here we obtain several new characterizations that provide algorithms for recognizing CO-graphs and obtaining their cyclic orientations in linear time. We show that the edge maximal CO-graphs are 2-trees; that is, G=(V,E) is a 2-tree if and only if G is CO and G^′=(V,E^′) is not CO whenever E is a proper subset of E^′.     

Dynamic analysis of aggregation of methylene blue with polarized optical waveguide spectroscopy

Polarized optical waveguide (POW) spectroscopy permits analysis of the changing molecular state of methylene blue (MB), including aggregate order and orientation at the waveguide surface. Monomer or dimer, dissolved randomly in MB aqueous solution, tends to aggregate at the waveguide surface during air drying. Furthermore, POW spectroscopy dynamically revealed that MB molecules became oriented vertically to the waveguide surface with increasing aggregation order.     

Magnetic material arrangement in oriented termites: a magnetic resonance study

Temperature dependence of the magnetic resonance is used to study the magnetic material in oriented Neocapritermes opacus (N.o.) termite, the only prey of the migratory ant Pachycondyla marginata (P.m.). A broad line in the g=2 region, associated to isolated nanoparticles shows that at least 97% of the magnetic material is in the termite’s body (abdomen + thorax). From the temperature dependence of the resonant field and from the spectral linewidths, we estimate the existence of magnetic nanoparticles 18.5 ± 0.3 nm in diameter and an effective magnetic anisotropy constant, K_eff between 2.1 and 3.2 × 10⁴ erg/cm³. A sudden change in the double integrated spectra at about 100 K for N.o. with the long body axis oriented perpendicular to the magnetic field can be attributed to the Verwey transition, and suggests an organized film-like particle system.     

Properties of blends containing two liquid crystalline polymers

Blends containing two, wholly aromatic, naphthalene-based liquid crystalline polymers (LCPs) are studied. Experimental results show that the viscosities of the resulting blends are lower than the parent LCPs over the entire shear-rate range investigated. The orientation development following capillary flow demonstrates, that over a defined blend composition range, some blends have higher orientability than the constituent polymers. This is further manifested in the tensile and flexural properties of injection-molded specimens. A detailed analysis indicates that in the composition range where synergistic effects are observed in orientation development as well as in mechanical properties, only one glass transition temperature is detected. This suggests that “miscibility” is desirable for obtaining maximum properties in these blend systems.     

PNL分子在正、负电性纳米银上的吸附取向

制备了两种不同电性的纳米银粒子的脉体,发现当邻菲罗啉分子分别吸附在这两种纳米银上时,其表面增强喇曼谱有明显的不同.在正电性纳米银上,面外弯曲模式受到增强,而在负电性纳米银上,面内伸缩模式受到增强,通过分析增强谱的差异表明,分子在这两种不同电性胶态纳米银表面上可能分别以平躺及站立方式吸附.     

Influence of particle orientation on retrieving cirrus cloud properties by use of total and polarized reflectances from satellite measurements

The influence of ice crystal orientation was investigated on retrieving cirrus optical thickness (τ) and aspect ratio of ice crystals (Q) from satellite measurements using the total and polarized reflectances at a wavelength of . We considered columnar and plate like hexagonal ice crystals whose long axes are randomly oriented in the horizontal plane (2D model) with some amplitude of oscillation expressed by a Gaussian distribution function with the standard deviation of σ.The retrieved τ and Q values significantly depend on the assumption of σ, in particular for the plate type. Furthermore, the relationship between σ and the retrieved values depends on the solar, satellite, and target geometries. In our case study, for one target area, τ value retrieved using the 2D model with σ=5° was approximately twice larger than that using the 2D model with σ=20°, while the retrieved Q value was not significantly influenced by σ. For another target area, the τ(Q) retrieved using the 2D model with σ=5° was about 1.5 (1.8) times larger than that retrieved using the 2D model with σ=20°.     

Description of the state of deformation of ethylene–tetrafluoroethylene alternating copolymer films estimated by using a model proposed in terms of orientation of crystallites within a rod

To study the deformation mechanism of ethylene–tetrafluoroethylene alternating copolymer films caused by elongation, a model relating crystal orientation to the orientation of the rods was proposed. The orientation distribution of crystallites within the rod was given as the correlation with the rod orientation. The distribution functions of a given reciprocal lattice vector of the crystal plane were derived from the two functions of the crystallites and of rods with several parameters representing the orientation of rods and the rotation of crystallites within a rod. By choosing suitable values of the parameters, the calculated functions were in good agreement with the results of X-ray diffraction experiments. From the values of the parameters to give the best fit between calculated and observed results, it turned out that the characteristic orientation of the c-axis is mainly due to the preferential orientation of the rod with respect to a stretching direction and is hardly affected by the rotation of crystallites within the rod. Using the two orientation functions concerning rods and crystallites, Hv light scattering was formulated by introducing an interparticle interference effect of the rods. The calculated results assumed the characteristic profile of the observed patterns as the superposition of broadleaf lobes and a sharp pattern of streaks. Received: 28 April 2000 Accepted: 30 September 2000     

用非偏振拉曼光谱表征聚合物的取向行为

采用非偏振激光为拉曼光源表征了聚丙烯纤维、尼龙6扁丝以及聚乙烯管材等3种取向的聚合物样品。实验表明,当入射光作用于样品的不同面(方向)时,所得到的拉曼光谱存在明显的差异。这一结果为表征聚合物取向开创了新思路,并拓宽了拉曼光谱技术的应用范围。     

Carbon-content dependent effect of magnetic field on austenitic decomposition of steels

The transformed microstructures of the high-purity Fe-0.12C alloy and Fe-0.36C alloy heat treated without and with a 12 T magnetic field have been investigated to explore the carbon-content dependent field effect on austenitic decomposition in steels. Results show that, the field-induced transformed morphology characteristics in different alloys differ from each other. In the Fe-0.12C alloy, the pearlite colonies are elongated along the field direction, and shaped by the chained and elongated proeutectoid ferrite grains in the field direction. However, in the Fe-0.36C alloy, the field mainly reduces the amount of Widmänstatten ferrite and elongates the formed proeutectoid ferrite grains in the field direction. No clear field direction alignment is obtained. The magnetic field also demonstrates carbon-content dependent effect on the texture of the formed ferrite. It clearly enhances the 〈001〉 fiber of the ferrite in the transverse field direction in the Fe-0.36C alloy. This field effect is related to the crystal lattice distortion induced by carbon solution and this impact becomes stronger with the increase of the carbon content. For the Fe-0.12C alloy, this field effect is greatly reduced due to the reduced carbon oversaturation in ferrite and elevated formation temperature. The orientation relationships (ORs) between the pearlitic ferrite and the pearlitic cementite in both alloys are less affected by the magnetic field. No obvious changes in the either type of the appearing ORs and their number of occurrences are detected.