Die swell behavior of liquid crystalline mesophase pitch

Die swell of a spinnable mesophase pitch was explored using a fiber spinning apparatus with varied capillary geometries and processing conditions. It was found that the die swell decreased with increased shear rate and increased with a rise of temperature. A nearly constant die swell value can be reached as shear rate gets high enough for different temperatures, and it decreased with increased die angles, but maintained unchanged for capillaries with different length-to-diameter ratios. For orifice die, the die swell ratios were found to be affected little by the extrusion rate and the temperatures. The texture examination of the extrudates from orifice die and dies with capillaries shows that the extensional flow produces high molecular orientation, and the shear flow-induced tumbling might store elastic energy that will be recovered at the die exit.     

Novel bolaamphiphilic pyrimidinophane as building block for design of nanosized supramolecular systems with concentration-dependent structural behavior

A new macrocyclic bolaamphiphile with thiocytosine fragments in the molecule (B1) has been synthesized and advanced as perspective platform for the design of soft supramolecular systems. Strong concentration-dependent structural behavior is observed in the water-DMF (20% vol) solution of B1 as revealed by methods of tensiometry, conductometry, dynamic light scattering, and atomic force microscopy. Two breakpoints are observed in the surface tension isotherms. The first one, around 0.002 M, is identified as a critical micelle concentration (cmc), whereas the second critical concentration of 0.01 M is a turning point between the two models of the association involved. Large aggregates of ca. 200 nm are mostly formed beyond the cmc, whereas small micelle-like aggregates exist above 0.01 M. The growth of aggregates between these critical points occurs, resulting in a gel-like behavior. An unusual decrease in the solution pH with concentration takes place, which is assumed to originate from the steric hindrance around the B1 head groups. Because of controllable structural behavior, B1 is assumed to be a candidate for the development of biomimetic catalysts, nanocontainers, drug and gene carriers, etc.     

煤系中间相成形过程中的共熔效应

煤焦油沥青甲苯可溶物(TS)和废聚苯乙烯(WPS)共炭化生成的中间相沥青,性能得到很大改善.可溶性中间相的质量分数从10%提高到52%,光学结构从中间相体积分数65%的粗镶嵌结构改善为:100%的广域融并体;表观黏度分析显示添加WPS后,中间相沥青从触变性变为非触变性.红外和核磁共振分析表明共炭化过程中发生烷基化反应,出现较多的α亚甲基结构.X射线衍射结果显示在添加WPS后使芳香平面分子取向排列变好.结果表明:共炭化过程中,烷基结构的增多是共熔效应发生的主要原因.     

中间相炭微球/活性炭复合材料的电化学行为

以中间相炭微球( CMS)为核心材料,沥青为壳层材料前躯体,采用原位生成法制备了中间相炭微球/活性炭(AC)复合材料.将所制CMS/AC复合材料作为超级电容电池的负极材料,组装了模拟电容器和锂离子半电池.采用扫描电镜和X-射线衍射仪分析了材料的物理结构,并研究了CMS/AC复合材料的电化学行为进行研究.结果表明:CMS/AC复合负极材料在六氟磷锂/碳酸乙烯酯+碳酸二甲酯(LiPF6/EC+DMC)与四氟硼酸四乙基铵/乙腈( Et4 NBF4/AN)电解液中均表现出良好的电化学性能,其比电容在模拟电容器中达到25.8 F/g,在锂离子半电池中能达到306.6 mAh/g (0.2C);同时表现出良好的倍率性能和循环性能.     

Three-dimensional thermal conductive behavior of graphite materials sintered from ribbon mesophase pitch-based fibers

Block graphite prepared from ribbon mesophase pitch-based fibers, which are arranged unidirectionally, exhibits three-dimensional anisotropic thermal conductive behavior. The thermal conductivity (TC) of the graphite along the direction parallel to the fiber axis is 30-40× that of the other two directions. And with increasing graphitization temperature, the TC of the graphite material treated at 3273 K in the direction parallel to the fiber axis increases and reaches 837 W m⁻¹ K⁻¹, while that in other direction decreases to 11 W m⁻¹ K⁻¹ because of regular arrangement of graphite crystallites.     

Tailoring structures and properties of mesophase pitch-based carbon fibers based on isotropic/mesophase incompatible blends

Blends composed of isotropic and mesophase pitches in various proportions were used as precursors for carbon fibers. The effects of composition on the morphology of blends, precursor spinnability, transversal texture, and mechanical properties of the final carbon fiber were studied. The blends are binary incompatible phase-separation systems. When the content of isotropic pitch is ≤30 %, it is distributed uniformly in the mesophase matrix as spheres; whereas, complete phase inversion occurs when the content is ≥35 %. Blends containing isotropic pitch in dispersion phase show good spinnability and small-diameter fibers can be continuously drawn. The transversal texture of carbon fibers is transformed from a radial type with a crack along the fiber axis to an intermediate morphology between radial and random type by blending 20–30 % isotropic pitch. The tensile strength of carbon fibers with 20–30 % IPc is 2.5 times as high as the AR-based CF without the reduction of Young’s modulus.     

Fullerene containing polymers: a review on their synthesis and supramolecular behavior in solution

Due to the theoretical importance and potential applications of fullerene, numerous fullerene derivatives have been developed to enhance its solubility and processability. This article provides an overview on fullerene containing polymers, from synthesis to their physicochemical properties in solution. Due to the unique chemical structure of fullerene, different fullerene containing polymeric architecture can be synthesized through various kinds of conjugating techniques, where fullerene can be located either on the backbone or the branch chain. Recently, the successful development of azido coupling and atom transfer radical addition (ATRA) makes it possible to synthesize "controlled" and well-defined fullerene containing polymers. Experimental results indicated that fullerene containing polymers not only increase the solubility of fullerene in solution, but also retain the conjugating properties of fullerene molecules. By blocking well-defined functional polymers onto fullerene molecules, different types of stimuli-responsive amphiphilic systems can be achieved. However, the large bulk volume and high hydrophobicity of fullerene gives rise to the large aggregates with different morphologies produced in solution, which can be tuned by changing external stimuli, such as pH, temperature, salt, and co-solvents. Interestingly, fullerene containing anionic polymers could induce the formation nano-scale fractal pattern, but not fullerene containing cationic polymers, which is evident from morphological studies.     

A structural study on the stabilization and enhancement of mesophase pitch fibre

The components of coal tar-derived mesophase pitch fibre and its blend with polyvinyl chloride (PVC) pitch were studied for chemical changes after the stabilization. Microanalyses, solubility and solid ¹³C NMR measurements were performed. The temperature was found to be very influential on the progress of the stabilization. At a temperature of 230° C, PVC pitch enchanced the oxygen uptake of both fusible pyridine soluble (PS) and non-fusible pyridine insoluble (PI) fractions in the pure mesophase pitch, so shortening the time required for complete stabilization and raising more rapidly the softening point of the PS fraction. More oxygen-containing functional groups, such as phenolic, ether, carboxylic and carbonyl groups, were formed in both fractions. It is noted that any increase in the aromatic ring size of the PI fraction is rather limited at this temperature. In contrast, stabilization of PVC pitch at a higher temperature of 300° C, accelerated the increase in PI without accelerating oxygen uptake of both fractions. Hence, the softening point of the remaining PS was unchanged or even lowered. An increase of aromatic ring size of the PI component by stabilization was marked at the higher temperature. Suggested stabilization schemes and the role of added PVC pitch in accelerating stabilization are discussed for each of these temperatures taking account of the above results.     

Effects of hydrogenation of petroleum pitch on mesophase formation

The effects of hydrogenation of petroleum pitch on mesophase formation have been studied in terms of the hydrogen donor (D _a) and acceptor (A _a) abilities of starting pitch, the temperature dependence of mesophase content, the thermal properties of the resultant mesophase pitches with differential scanning calorimetry (DSC), and ¹³C-NMR spectra of the mesophase pitches in the liquid and solid states. Hydrogenation of petroleum-derived pitch causes a significant increase of (D _a) and a clear shift of the mesophase generation temperature to the hightemperature side. Measurement of the characteristics of molecular size for mesophase pitches using DSC has been successfully accomplished. The increase of D _a due to hydrogenation cause the production of mesophase having a smaller average molecular size and a more homogeneous molecular size distribution. The decrease of molecular size in the mesophase seems to cause the narrowing of the characteristic peak for mesophase around 180 p.p.m. in ¹³C-NMR spectra in the liquid state.     

Surface effect on the elastic behavior of static bending nanowires

The surface effect from surface stress and surface elasticity on the elastic behavior of nanowires in static bending is incorporated into Euler-Bernoulli beam theory via the Young-Laplace equation. Explicit solutions are presented to study the dependence of the surface effect on the overall Young's modulus of nanowires for three different boundary conditions: cantilever, simply supported, and fixed-fixed. The solutions indicate that the cantilever nanowires behave as softer materials when deflected while the other structures behave like stiffer materials as the nanowire cross-sectional size decreases for positive surface stresses. These solutions agree with size dependent nanowire overall Young's moduli observed from static bending tests by other researchers. This study also discusses possible reasons for variations of nanowire overall Young's moduli observed.     

Fabrication strategies and supramolecular interactions of polymer-lipid complex nanoparticles as oral delivery systems

Nano Research - Oral administration of nutrient/drug is the most common and preferred route. However, a number of barriers are encountered after ingestion, limiting efficient oral nutrient/drug...     

The effect of metakaolin on the corrosion behavior of cement mortars

In this paper the effect of metakaolin addition on the corrosion resistance of cement mortar is studied. A poor Greek kaolin with a low kaolinite content was thermally treated and the produced metakaolin (MK) was ground to the appropriate fineness. In addition, a commercial metakaolin (MKC) of high purity was used. Several mixture proportions were used to produce mortar specimens, where metakaolin replaced either sand or cement. Mortar specimens were then exposed to the corrosive environment of either partial or total immersion in 3.5% w/w NaCl solution. For the evaluation of the performance of metakaolin, the following methods were used: compressive strength, corrosion potential, mass loss, electrochemical measurements of the corrosion rate by the Linear Polarization method, carbonation depth and porosity. It is concluded that metakaolin improves the compressive strength and the 10% w/w addition shows the optimum contribution to the strength development. In addition, the use of metakaolin, either as a sand replacement up to 20% w/w, or as a cement replacement up to 10% w/w, improves the corrosion behavior of mortar specimens, while when metakaolin is added in greater percentages there is no positive effect.     

On the effect of debonding on the overall behavior of composite materials

The present paper is an investigation of the effects of debonding on some of the basic properties of composite materials. In the adopted debonding model, the tractions and normal displacements are continuous at the interfaces, but there exists a jump in the tangential displacement, proportional to the corresponding shear traction. The consequences of such interface conditions on the inverse relation between the effective moduli and compliances are studied. By means of a simple example of a laminated medium, it is shown that the inverse relation ceases to be valid in this composite as the degree of debonding increases. This phenomenon is explained by investigating the rate of decay of end effects, and thus the applicability of Saint-Venant principle, in a laminated composite with debonding.     

不同杂化离子对电聚合聚苯胺电容行为的影响

用原位电聚合的方法在不锈钢电极(SS)上制备出了由ClO-4,SO2-4,NO-3,BF-4,TsO-(对甲苯磺酸根)等离子杂化的聚苯胺(PANI)(厚度5～10μm).扫描电镜表明不同的杂化离子对聚苯胺的表面形貌产生了很大影响,分别产生了纳米多孔、颗粒、纤维等多种表面结构.循环伏安研究表明,由硫酸根和高氯酸根离子杂化...     

由中间相沥青制备泡沫炭:Fe(NO3)3的影响

以中间相沥青为前驱体制备高性能泡沫炭，在考察中间相沥青、Fe（NO3）3及其混合物热分解行为的基础上，着重研究了Fe（NO3）3对制备中间相沥青基泡沫炭的影响，揭示了Fe（NO3）3对泡沫炭孔泡结构的影响规律及其作用机制，初步研究了在泡沫炭炭化过程中形成的Fe／C之物相结构及其石墨化行为。结果表明，在不同的炭化温度下，Fe在泡沫炭中的存在形态各异；Fe物种的存在有利于提高泡沫炭的石墨化程度。     

Breakthrough behavior of diethyl sulphide vapor on active carbon systems

Breakthrough behavior of diethyl sulphide vapors on carbon systems such as active carbon, NaOH/CrO3/C, NaOH/CrO3/EDA/C and RuCl3/C has been studied by using modified Wheeler equation and the same was used to calculate the pseudo-first-order rate constant (kv) and kinetic saturation of capacity (W(e)) values. Effects of various parameters such as bed height, air flow rate, concentration and temperature on the above parameters have also been studied. Rate constant was found to be increasing with air flow rate, while W(e) was found to be invariable. Both kv and W(e) decreased with the increase in temperature, however, no significant effect on W(e) and kv was observed due to concentration change. The values of kinetic saturation capacity were used to predict the service lives/breakthrough times of carbon beds (when used in filtration systems).     

Optimization of the preparation conditions of polygranular carbons from mesophase

Polygranular carbons were prepared from a coal-tar pitch based mesophase by sintering, using different experimental conditions. The temperature and time of mesophase stabilization, the pressure applied during moulding, and the sintering heating rate were investigated in order to obtain materials with optimum properties. Oxidative stabilization with air between 225 and 250°C causes a significant reduction in the plasticity of the coal-tar pitch based mesophase, allowing moulding and sintering to be performed. An increase in the moulding pressure results in an increase in the bulk density of the green materials. However, sintering must be carried out at low heating rates in order to control the release of gases and thus avoid damage to the sintered material. Higher sintering heating rates are compatible with low moulding pressures and a high degree of stabilization. Whenever the materials do not distort during sintering, a common feature observed is that mechanical and electrical properties improve with increasing moulding pressure, while an increase in sintering heating rate only serves to improve the strength of the materials.     

Chitosan formulations for steroid delivery: effect of formulation variables on in vitro characteristics

Chitosan film formulations for steroid delivery after craniomaxillofacial surgery were formulated by using three different types of chitosan with respect to their molecular weight as low, medium and high. Film formulations were prepared by casting/solvent evaporation technique. In vitro characterization, film thickness, equilibrium swelling degree, in vitro release profiles and surface morphologies were investigated. For two different types of crosslinkings, the release of dexamethasone sodium phosphate (DSP) can be extended as the molecular weight increases. As a result, chitosan film formulations should be beneficial for steroid delivery for a certain time after craniomaxillofacial surgery.