漫谈原子量的质谱法测定──纪念《大学化学》创刊十周年

漫谈原子量的质谱法测定──纪念《大学化学》创刊十周年张青莲（北京大学化学学院１００８７１）原子量［１］是某元素一个原子的平均质量与一个１２Ｃ原子质量的１／１２之比。原子量Ａｒ（Ｅ），或称相对原子质量［２］，其现代测定方法是根据公式：Ａｒ（Ｅ）。设元素...     

热处理对聚醚醚酮晶体结构参数及结晶度的影响

采用广角Ｘ射线衍射（ＷＡＸＤ）方法研究了不同热处理温度下聚醚醚酮（ＰＥＥＫ）的晶胞参数、微晶尺寸及结晶度的变化。根据Ｘ射线散射强度理论，运用图解多重峰方法导出了以ＷＡＸＤ方法计算ＰＥＥＫ结晶度的公式；用此公式对经不同热处理的ＰＥＥＫ样品进行计算，结果与由密度法及量热法测定的结果具有较好的可比性。     

PEEK碳纤维增强复合材料的动态力学行为

ＰＥＥＫ碳纤维增强复合材料的动态力学行为李健（中国科学院固体物理研究所合肥２３００３１）章明秋，徐建军（中山大学材料科学研究所广州）（青岛化工学院青岛）关键词ＰＥＥＫ，碳纤维复合材料，内耗，Ｔｇ热塑性、耐高温的工程塑料聚醚醚酮（ＰＥＥＫ）是一种半晶聚...     

原子簇P12（D3d）的理论研究

利用Ｇａｕｓｓｉａｎ－９２程序在６－３１Ｇ基组下优化Ｐ１２（Ｄ３ｄ）构型，研究了３Ｐ４（Ｔｄ）→Ｐ１２（Ｄ３ｄ）的相对能量，计算结果为△Ｅ＝Ｅｐ１２（Ｄ３ｄ）－３Ｅｐ４（Ｔｄ）＝－７９．８４４ｋＪ／ｍｏｌ，优化Ｐ１２（Ｄ３ｄ）获得的Ｐ－Ｐ键键长接近于实验测得的Ｐ－Ｐ单键键长，并进一步在该基组下计算了Ｐ１２（Ｄ３ｄ）原子簇的振动频率，得到的全部为正频率，表明原子簇Ｐ１２的Ｄ３ｄ构型是位能面上的稳定点     

聚氧化乙烯和聚醋酸乙烯酯共混热力学参数的理论估算

实验测定了聚氧化乙烯（ＰＥＯ）和聚醋酸乙烯酯（ＰＶＡｃ）的共混热以及共混组分的热压系数和热膨胀系数．并由上述实测值计算了状态方程参数．用Ｈａｍａｄａ~［１－２］等改进的Ｆｌｏｒｙ状态方程理论估算了ＰＥＯ／ＰＶＡｃ混体系的交换能参数（Ｘ_１２）、相互作用参数（ｘ_１２／ｒ_１）和剩余混合体积（Ｖ~Ｅ／Ｖ~０）．     

多壁碳纳米管对PS分子量影响的研究

由于碳纳米管（CNT）具有优异的力学、电学、光学等性能，近年来，聚合物／碳纳米管（polymer／CNT）复合材料的研究已经成为研究者关注的热点。相关的研究主要集中在：一是将CNT作为填充材料制各复合材料，使复合材料的力学、电学等性能得到提高。二是将CNT作为主体，用聚合物对CNT进行修饰，使CNT在有机溶剂中能够获得良好的溶解度。而对于在聚合反应中，CNT的加入对聚合物分子量影响的研究，相关的报道较少。本文利用悬浮聚合法制备了聚苯乙烯／多壁碳纳米管（PS／MWNT）复合材料，采用透射电镜（TEM）和凝胶渗透色谱（GPC）对其进行了分析，详细研究了MWNT对于PS分子量的影响。     

Wade规则在稠合型硼烷等中的应用

本文把Ｗａｄｅ规则推广应用于稠合型硼烷和稠合型金属碳硼烷中,导出计算它们价电子数（ＮＶＥ）的公式。对于稠合型硼烷,本文公式与唐敖庆等的拓扑结构规则的计算结果相同。但本文公式的适用范围比上述两个规则广。     

聚氯乙烯—聚氧乙烯共混物的反相色谱研究

用反相色谱研究了聚氯乙烯与聚氧乙烯的相容性，发现其共混物的经保留体积Ｖｇ２３具有重量加和性，表明共混物可能发生了相分离，导出了相分离体系聚合物相互作用参数Ｘ２３的近似关系式：ｘ２３＝（ｘ１２－ｘ１３）＾２／２，由此式可以解释ｘ２３对探针种类的依赖性，聚氯乙烯和聚氧乙烯共混体系的反相色谱实验结果基本符合这一关系式。     

颗粒填充复合材料的界面层研究

运用动态力学方法研究了硅粉和Al2O3填充的环氧树脂基复合材料的力学性能，结果表明当填料含量超过20phr时，随着填料含量的增加，复合材料的玻璃化转变温度Tg逐渐移向高温区，损耗峰的半高宽度W1／2趋于增宽。当填料含量在20phr时，损耗峰的高度和半高宽度W1／2分别有一个突跃式的下降和增宽，而且Tg大于纯环氧体系。利用WLF方程对环氧复合材料的模－温度关系进行了理论推算，结果表明用WLF方程预估这类复合体系在Tg附近的模量是可行的。     

胺固化端环氧基二硅氧烷动力学及性能研究

合成了１，３－二甲基－１，３－二乙基－１，３－双［３－（２，３－环氧丙氧基）丙基］二硅氧烷（ＴＥＤＳ）．对其与二正丁胺的模型反应、与ＤＤＭ（４，４’－二氨基二苯基甲烷）的固化反应劝力学研究表明，反应对ＴＥＤＳ为一级反应．ＴＥＤＳ改性环氧Ｅ—５１体系的动态力学性能、冲击性能和形态结构的研究表明，随改性体系中ＴＥＤＳ含量的增加，体系的玻璃化温度是线性下降、冲击强度增大、冲击试样的断裂面渐渐显现出韧性断裂的特征．     

The influence of the mesophase on the transverse and longitudinal moduli and the major poisson ratio in fibrous composites

Expressions for the evaluation of the transverse and longitudinal elastic moduli and the major Poisson ratio of unidirectional fiber composites are derived. The model described is based on the correct version of Kerner's model, which in our case is conveniently modified by introducing a mesophase layer between the fiber and the matrix in the representative volume element surrounding the typical fiber. The expression for the longitudinal elastic modulus derived in this paper, and the law of mixtures already presented in previous papers, give concordant results. Therefore, the law of mixtures, taking the mesophase also into account, and the two-term unfolding model for the mesophase are used for the evaluation of its extent and its properties. The model was applied to a glass filament-epoxy resin composite and its predictions were found to be in good agreement with the experimental data.     

Experimental investigation on mechanical properties of unidirectional and woven fabric glass/epoxy composites under off-axis tensile loading

Mechanical properties of unidirectional (UD) and woven fabric glass/epoxy composites under off-axis tensile loading were experimentally investigated. A number of off-axis tests considering different fibre orientations were performed to study the character and failure mechanisms of the composite laminates. The experimental results indicated that both off-axis elastic moduli and strength degrade with increasing off-axis angle in all cases, and the woven fabric composites present nonlinear stress-strain behaviour under off-axial tension loading. The Tsai-Wu criteria used for failure analysis of the UD and woven fabric composites were compared and discussed, especially considering different values of interaction coefficient F₁₂. The prediction results demonstrated that the Tsai-Wu criterion can be used successfully to analyse failure properties of the woven fabric composites under multiaxial stress conditions, where the criterion with the modified coefficient F₁₂ obtained from the 45° off-axial tension tests is better and has higher accuracy. Finally, the specific failure modes were compared in the UD and woven fabric composites. The selected fracture surfaces were also observed by scanning electron microscopy (SEM), and the corresponding failure mechanisms of the woven fabric composites under off-axis tensile loading were identified.     

Mechanical behavior of basalt and glass textile composites at high strain rates: A comparison

The aim of this paper is to study and compare the mechanical behavior of woven basalt and woven glass epoxy composites at high strain rates, in order to assess the possibility of replacing glass fiber composites with basalt fiber composites for aircraft secondary structures, such as radomes, fairings, wing tips, etc. Both composites were produced using the same epoxy matrix, the same manufacturing technique, and with comparable densities, fiber volume fractions, and static stiffnesses. Dynamic tensile and shear experiments were performed using a split Hopkinson tension bar, in addition to reference quasi-static experiments to compare both material behaviors over a wide range of strain rates. Normalized results with respect to the material density and fiber volume fraction showed that basalt epoxy composite had higher elastic stiffness, ultimate tensile strength, ultimate tensile strain, and absorbed energy in tension compared to glass epoxy composite. This suggests a promising potential in replacing glass fibers composites with basalt fiber composites in aircraft secondary structures and, more generally, components prone to impact. However, for the basalt epoxy composite, improvements in the fiber-matrix adhesion and in the manufacturing technique are still required to enhance their shear properties compared to glass fiber composites, and fully exploit the potential of basalt epoxy composites in aeronautical applications.     

Low velocity impact and pseudo-ductile behaviour of carbon/glass/epoxy and carbon/glass/PMMA hybrid composite laminates for aircraft application at service temperature

Carbon/glass hybrid composite (CGHC) laminates are some of the most promising composites for lightweight applications. Sometimes these laminates are used in warm environment, such as aircraft frame structures, and this may affect their performance. In order to investigate this issue, the present research aims to study the effect of temperatures on the impact behavior and pseudo-ductile behaviour of CGHC in presence of different types of thermosets “epoxy” and thermoplastic “acrylic poly-methyl methacrylate-PMMA”. The experiments were started with making of CGHC laminates from different stacking sequences of unidirectional carbon and woven glass fibre layers, using a vacuum-assisted resin transfer method followed by curing treatment. In addition to CGHC laminates, four other neat batches (Carbon/epoxy, Carbon/PMMA, Glass/epoxy, Glass/PMMA) were prepared for comparison. The low velocity impact behaviour of the fabricated panels was evaluated at high temperatures (60 °C and 80 °C) according to ISO 6603-2 standard, using drop tower, while pseudo-ductile behaviour and ductility index (DI) of the specimens were estimated based on the measured total energy and elastic energy. Also, the low-velocity impact response was modeled mathematically based on a modified energy-balance model to predict the absorbed energies. Finally, the failure mechanisms were examined using optical microscope to determine the influence of these damage growth on DI of the composites under different temperatures. The results showed that the impact energy response of both hybrid composites i.e. epoxy and PMMA was stable even as the temperature rose, however, carbon/glass/PMMA exhibited better performance compared with carbon/glass/epoxy with an increase in impact energy response estimated at 50% (25 °C) and 53% (80 °C). Also, the pseudo-ductile phenomenon was strongly evident, which facilitates the predictablility of failure.     

In situ thermoset molecular composites

The polymerization of rigid rod polymer precursors in a reactive matrix precursor, which is later cured in the mold, constitutes the in situ process. A poly-azomethine (PAM) was used as the rigid rod molecule. The resin used was an epoxy. We discuss the prediction of mechanical properties using micromechanics equations for chopped fiber composites. The chemistry used to synthesize the rigid rod polymer PAM in the epoxy precursor is reviewed. Approaches to better control the cure of these epoxy systems through cure kinetics and cure rheology studies completes the thermoset in situ molecular composite process. There was a 71% increase in tensile modulus in comparison to that of the neat epoxy resin. Molecular modeling simulations and continuum mechanics are used to help understand these findings. PAM/epoxy systems were used as a matrix material in the fabrication of unidirectional glass fiber/(PAM/epoxy) structural composites. © 1994 John Wiley & Sons, Inc.     

Investigation of a waterborne epoxy for E‐glass composites

We present a continuing investigation of epoxies based on diglycidyl ether of bisphenol A cured with 2‐ethyl‐4‐methylimidazole in the presence of the nonionic surfactant Triton X‐100. Interest in this epoxy system is due partially to its potential application as a waterborne replacement for solvent‐cast epoxies in E‐glass‐laminated printed circuit boards. The surfactant additive could potentially alter the interfacial properties and durability of composite materials. Previous studies revealed that the viscoelastic behavior of the cured epoxy is altered when it serves as the matrix in a glass‐fiber‐reinforced composite. The additional constraining and coupling of the E‐glass fibers to the segmental motion of the epoxy matrix results in an apparent increased level of viscoelastic cooperativity. Current research has determined that the cooperativity of an epoxy/E‐glass composite is also sensitive to the surface chemistry of the glass fibers. Model epoxy/E‐glass composites were constructed in which the glass was pretreated with either 3‐aminopropyltriethoxysilane or 3‐glycidoxypropyltrimethoxysilane coupling agents. Dynamic mechanical analysis was then used to create master curves of the storage modulus in the frequency domain. The frequency response of the master curves and resulting cooperativity plots clearly varied with the surface pretreatment of the glass fibers. The surfactant had surprisingly little effect in the observed trends in the cooperativity of the composites. However, the changes in cooperativity due to the surface pretreatment of the glass were lessened when the samples were prepared from waterborne emulsions. Moisture‐uptake experiments were also performed on epoxy samples that were filled with spherical glass beads as well as multi‐ply laminated composites. No increases in the diffusion constant could be attributed to the surfactant. However, the surfactant did enhance the final equilibrium moisture‐uptake levels. These equilibrium moisture‐uptake levels were also sensitive to the surface pretreatment of the E‐glass. © 2000 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 38: 2351–2365, 2000     

Environmental degradation of E‐glass/nanocomposite under the combined effect of UV radiation,moisture, and rain

This study seeks to investigate how the enhanced properties of the nanoclay E‐glass/epoxy composite can withstand the combined effects of ultraviolet radiation, moisture, and rain. The montmorillonite nanoclay's affinity to moisture compounded the moisture absorption ability of the nanoclay E‐glass/epoxy composites. The moisture in the polymer structure caused delamination, debonding of the fibers/matrix, microvoids, and fiber pullouts. The high clay content (2 wt %), therefore, recorded the highest rate of degradation of 15% in flexural stress for the first 20 days, compared to about 8 and 6% loss for the unmodified (0 wt %) and 1 wt % composites respectively. However, as the aging progressed beyond 20 days, the rate of degradation of the nanoclay E‐glass/epoxy composites laminates was steady at 10 and 18%, respectively, for the 1 and 2 wt %, while that of the unmodified polymer continued to degrade progressively. On the contrary, the viscoelastic properties of the nanoclay E‐glass/epoxy composites continued to deteriorate at a faster rate than the unmodified polymer composite. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1024–1029     

A mesoscale study of thermal expansion behaviors of epoxy resin and carbon fiber/epoxy unidirectional composites based on periodic temperature and displacement boundary conditions

The thermal expansion behaviors of neat epoxy resin and carbon fiber/epoxy unidirectional (UD) composites were experimentally and numerically studied in this paper. The dynamic mechanical analysis (DMA), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and thermal conductivity measurement were used to measure the thermo-mechanical properties of epoxy resin at different temperatures. The dilatometer was used to measure the thermal strains and linear CTEs of neat epoxy resin and UD composites. In addition, a mesoscale finite element model based on the periodic temperature and displacement boundary conditions was presented to analyze the thermal expansion behaviors of UD composites. The resin-voids representative volume element (RVE) was used to calculate the thermo-mechanical properties of several kinds of resin-voids mixed matrix. From the results it can be found that the glass transition temperature of epoxy resin, porosity and fiber orientation angle have significant effects on the thermal expansion behaviors of UD composites. The mesoscale finite element analyses (FEA) have obvious advantages than various existing analysis models by comparing their predictive results. The distributions of thermal displacement, thermal stress and thermal strain were extracted between the carbon fiber, resin-voids mixed matrix and their interface, and also between the front and back surfaces of the loading direction, to further investigate thermal expansion structure effects of UD composites. This paper revealed that the mesoscale FEA based on periodic temperature and displacement boundary conditions can be also used for thermal expansion researches of other complex structure composites.     

Effect of phase change microcapsules on the thermo-mechanical,fracture and heat storage properties of unidirectional carbon/epoxy laminates

This work aims at producing and characterizing unidirectional carbon/epoxy composites containing different fractions of paraffin microcapsules (MC) for thermal management applications. The viscosity of the epoxy/MC mixtures increases with the MC content, thereby increasing the final matrix weight and volume fraction and reducing that of the fibers. This is at the basis of the decrease in mechanical properties of the laminates with high MC concentration (the elastic modulus decreases up to 53% and the flexural strength up to 67%), but the application of theoretical models shows that this decrease is only due to the lower fiber volume fraction, and not to a change in the properties of the constituents or the fiber/matrix interaction. The MC phase is preferentially distributed in the interlaminar zone, which leads to a thickening of this region and a decrease in matrix-related properties, such as the interlaminar shear strength, which decreases of up to 70%. However, a modest MC fraction causes an increase in the mode I interlaminar fracture toughness of 48%, due to the introduction of new toughening mechanisms. On the other hand, an excessive MC content lets the crack propagating through the matrix and not at the fiber/matrix interface, thereby reducing the toughening mechanism provided by fiber bridging. For the thermal properties, the phase change enthalpy increases with the MC fraction up to 48.7 J/g, and this is reflected in better thermal management performance, as proven by thermal imaging tests. These results are promising for the development of multifunctional polymer composites with thermal energy storage and thermal management properties, and future works will be focused on a deeper study of the micromechanical properties of PCM microcapsules and on the improvement of the capsule/matrix adhesion.     

Comparison between 3-point bending and torsion methods for determining the viscoelastic properties of fiber-reinforced epoxy

Dynamic mechanical analysis is a technique used to determine the viscoelastic properties of polymers and their composites. The storage modulus, loss modulus and loss factor in correlation with the glass transition temperature can be detected by several means. In this study, these properties are determined using a dynamic mechanical analyzer in 3-point bending mode, as well as a rheometer in torsion mode. The materials under consideration are a unidirectional glass fiber-reinforced epoxy, a quasi-isotropic carbon fiber-reinforced epoxy and a quasi-isotropic glass fiber-reinforced epoxy. The results of each method and material are presented and the advantages and limitations of each method are discussed. 3-point bending proved to be more suitable to detect the effect of fiber orientation for unidirectional fiber-reinforced epoxy but requires careful control of sample dimensions for accuracy. Torsion, on the other hand, gave consistent measurements for samples of varying lengths, proving to be a suitable method if materials are scarce and limited.