活性碳和5A分子筛的吸附特性及其在真空获得中的作用

评述了活性碳和５Ａ分子筛的吸附等温线及其在真空佩温绝热夹层真空获得中的作用。分析了真空夹层抽真空除气时用Ｎ＿２气置换以及用“多次吸附－脱附Ｎ＿２气”方法活化吸附剂等先进工艺的机理。论述了根据吸附剂吸水的吸附等温线，合理确定活化工艺条件的方法。     

裂纹对石墨烯拉伸力学性能影响的数值仿真

为研究裂纹对石墨烯力学性能的影响,以锯齿型石墨烯为研究对象,基于分子动力学方法,采用Tersoff势函数分析裂纹长度对石墨烯拉伸力学性能的影响以及含有裂纹的石墨烯在不同应变率下的拉伸变形破坏过程.结果表明,裂纹长度的增加大大减小石墨烯的抗拉强度和抗拉应变,对弹性模量有一定影响;裂纹降低石墨烯的抗拉应变对应变率的敏感性,但对于含有裂纹的石墨烯,仍可以增大加载速率来提高石墨烯的抗拉性能.     

Viscosities of nonelectrolyte liquid mixtures. I. binary mixtures containing p-dioxane

Viscosity measurements are reported for p-dioxans with cyclohexane, n-hexane, benzene, toluene, carbon tetrachloride, tetrachloroethane, chloroform, pentachloroethane, and ethyl acetate at 303.15 K. Excess Gibbs energies of activation G ^*E of viscous flow have been calculated with Eyring's theory of absolute reaction rates. The deviations of the viscosities from a linear dependence on the mole fraction and values of G ^*E for binary mixtures have been explained in terms of molecular interactions between unlike pairs. The Prigogine-Flory-Patterson theory has been used to estimate the excess viscosity, ln , and corresponding enthalpy ln _H, entropy ln _S, and free volume ln _v terms for binary mixtures of p-dioxane with cyclohexane, n-hexane, benzene, toluene, carbon tetrachloride, and chloroform. Estimates of excess viscosities from this theory for p-dioxane with benzene, toluene, and carbon tetrachloride are good, while for the other three mixtures they are poor. The local-composition thermodynamic model of Wei and Rowley estimates the excess viscosity quite well even for p-dioxane mixtures with cyclohexane and n-hexane.     

Synthesis and characterization of aromatic polyisoimides derived from PMDA and para-diamines. An approach to in situ generated rigid-rod molecular composites

A new concept for the processing and fabrication of rigid-rod molecular composites aiming at the elimination or minimization of phase separation is proposed. This approach calls for a coil-like aromatic polyisoimide which is soluble and compatible with an amorphous matrix polymer or thermosettable oligomer and can undergo facile transformation to the corresponding rigid-rod polyimide in solid composite state, thus imparting the inherently high strength/high modulus properties to the final form. To this end, various synthetic routes were explored to obtain para-diamines which could afford high molecular weight and aprotic-solvent-soluble polyisoimides upon polymerization with pyromellitic dianhydride (PMDA). Four such polyisoimides were prepared, with their inherent viscosities ranging from 0.25 to 1.89 dl g⁻¹ in dimethylacetamide at 30°C. Facile thermally induced isoimide-imide conversion was demonstrated by solid-state (film) Fourier transform infrared spectroscopy. A preliminary evaluation of the compatibility of the polyisoimide/matrix resin was made. In one instance, a film prepared from the polyisoimide derived from PMDA and 3,3′,5,5′-tetramethylbenzidine (TMB) showed no visually detectable phase separation.     

Transitions of saturated monoacid triglycerides: Modeling conformational change at glycerol during α→β′→β transformation

The glycerol region geometry of modeled saturated monoacid triglycerides was altered by bond rotations and minor angle distortions to convert theoretical α-forms into bent β′- and β-forms. Direct α to β conversion involves lateral disruption of fatty chain packing to generate side-chain character typical of the β-form. Such disruption, which could contribute to fat bloom, allows additional molecular movement and shifts in molecular mechanics energy (MME) that may approximate thermal changes observed by differential scanning calorimetry during α to β transformations. Energy calculations at 100 points throughout each transformation identified plausible conversion routes. A two-stage conversion, α to either of two stereospecific β′-forms bent at glycerol followed by subsequent conversion to β, showed less chain movement and more favorable MME than direct α to β conversion. The preferred path, based on energy profiles of each conversion, involves a β′-D form and rotation of carbonyl to α-carbon bonds in chain #2 and a side chain (chain #3).     

Stochastic defect diffusion model for relaxation effects in crystalline polyethylene

It is suggested that some relaxation processes observed in crystalline polyethylene are consequences of the diffusive motion of a particular defect called a point dislocation or twist dispiration loop along the polyethylene stems in lamellar crystals. The motion of the defect, characterized by a diffusion coefficient and a mobility, is described by solutions of the Smoluchowski diffusion equation with boundary conditions that constrain the defect to move along routes that produce experimentally observable results. The fact that passage of the defect causes both a 180° rotation of the chain and moves an extra CH₂ group in the direction of the chain axis is important to the interpretation of the data according to this model. The diffusion coefficient for a defect is estimated to be around 2 × 10^?9 cm² s^?1 at 70°C. This value is shown to be reasonable both from the viewpoint of detailed computer modelling of defect motion and contemporary ideas about scaling.     

充油S-SBR加工行为的研究

在中试装置上合成相对分子质量分布较宽的充油S-SBR，考察不同环烷油和芳烃油填充量的充油S-SBR的流变性能和混炼行为。结果表明，增大油的填充量能提高充油S-SBR的流动性能，充芳烃油S-SBR相对于充环烷油的S-SBR对温度更敏感，宽相对分子质量分布的充环烷油S-SBR的混炼性能优于S-SBR1204及E-SBRl778，竟相对分子质量分布的充芳烃油S-SBR的混炼性能优于S-SBR1204，Solprene380和E-SBR1712。     

2,6-萘二甲酸二甲酯与一些二甲基萘所形成的激基复合物

2,6-萘二甲酸二甲酯与一些二甲基萘可以形成激基复合物。本文通过稳态和动态荧光光谱研究了这类激基复合物的形成与分子结构的关系。结果表明,尽管这些二甲基萘的电离能基本相同,但因取代基位置不同使分子中电荷分布不同,从而影响了激基复合物的形成能力。     

碳沉积法制富氮用炭分子筛的研究

本文提出的碳沉积法是用煤焦油馏分油的有机溶液浸渍煤炭化物,然后热解以进行“孔调变”。确定了最佳工艺条件,制得富氮性能良好的炭分子筛。并用D-A方程求取了各种样品的微孔结构参数。     

钛酸钾品须填充UHMWPE复合材料的摩擦磨损性能研究

用钛酸钾晶须(PTW)对超高摩尔质量聚乙烯(UHMWPE)进行填充改性,考察了复合材料的摩擦磨损性能,研究了其结晶情况,观察了磨损表面形貌并分析了其机理.结果表明随着PTW用量的增加,复合材料的硬度、结晶度以及维卡软化点都有所增大.PTW提高了复合材料的耐磨性,但摩擦系数有所上升.PTW的加入使得UHMWPE的磨损机理从黏着磨损和塑性变形改变成疲劳磨损和轻微的塑性变形,提高了其抗磨粒磨损的性能.