The melt elastic behavior of polypropylene/glass bead composites in capillary flow

The melt extrudate swell and entry pressure losses are important characteristics of elastic properties during die extrusion of polymeric fluids. They are usually expressed with die-swell ratio (B) and entry pressure drop (ΔP_o). In the present paper, the die-swell behavior and entrance pressure drop of a polypropylene (PP) filled with A-glass beads were investigated by using a Rosand capillary rheometer to identify the effects of the filler contents and extrusion rate on the elastic behavior of the sample melts. The experiments were carried out under the conditions with an apparent shear rate range of 50–10⁴ s⁻¹ and a temperature of 190 °C. The results showed that B increased nonlinearly with increasing shear rate at the wall (γ_w), and increased linearly with the increase of shear stress at the wall (τ_w). With the increase of the volume fraction of the fillers B decreased nonlinearly. Similarly, the entry pressure drop increased linearly with the increase of τ_w, whereas the influence of the filler concentration on ΔP_o was insignificant in this case. Furthermore, B increased as a linear function of ΔP_o, and extension stress (σ_e) increased nonlinearly with increasing γ_w.     

基于双尺度渐近分析的有限元算法

1．引言正如文山所说，由于复合材料和周期结构的材料系数ail（x）在局部区域内间断且跳跃性很大，加上区域内含有周期性洞穴或裂缝，且周期长度很小．一般而言，直接采用有限元方法进行数值模拟，其计算量大得惊人，甚至难以实现．文山针对这种特征，提出了一种可计算的双尺度渐近分析模式，本文在此基础上给出了相应的有限元算法，它包括：1．周期解在一个基本构造上的有限元计算；2．边界层的有限元计算．同时，给出了相应的误差分析．2．周期解的有限元计算首先考虑下列形式的边值问题；其中把，代E尸（on叫，iii（0关于E—（EI，ZZ…     

CL-20/TNT共晶炸药的分子动力学研究

运用分子动力学(MD)方法,选择凝聚态分子势能优化力场(COMPASS),对六硝基六氮杂异伍兹烷(ε-CL-20)、2,4,6-三硝基甲苯(TNT)晶体及其等摩尔比的CL-20/TNT混合炸药和共晶炸药进行不同温度下恒定粒子数等压等温(NPT)系综模拟研究.结果表明,CL-20/TNT共晶的内聚能密度(CED)和结合能随温度的升高逐渐减小;共晶的CED比混合炸药的大,结合能是混合炸药的2倍多,预示其稳定性明显增强.对相关函数和局部放大结构显示共晶中组分分子间作用主要来自TNT中H和CL-20中O以及CL-20中H和TNT中O之间形成的氢键.通过波动法求得的弹性力学性能结果表明,CL-20/TNT共晶的拉伸模量(E)、体积模量(K)和剪切模量(G)介于ε-CL-20和TNT晶体之间,且随温度的升高而下降,符合一般预期;但共晶炸药的柯西压(C12-C44,Cij弹性系数)、K/G和泊松比(ν)均比其组分炸药ε-CL-20和TNT高得多,预示该共晶具有异常高的延展性和弹性伸长,主要是二组分呈层状交替排列且之间存在较强相互作用所致.     

Dual emission of singlet and triplet states boost the sensitivity of pressure-sensing

Pressure-related sensing materials in mechanochromic luminescent materials have received wide attention. However, at present, most piezochromic luminescence (PCL) materials have problems such as aggregation-caused quenching (ACQ) effect due to the presence of powder form, complicated preparation methods and fluorescence quenching effect under high pressure. To solve these problems, we employ three components containing carbon dots (CDs), layered double hydroxides (LDHs) and polyvinyl alcohol (PVA) to construct the CDs-LDHs/PVA film. The LDHs can provide a rigid environment for CDs and improve the luminescent efficiency of CDs. The film shows high sensitivity, stability and reversibility. Moreover, the compressed film can recover to its original state by heating. Therefore, the PCL film with dual emission (fluorescence and phosphorescence) characteristic is constructed, which boosts the sensitivity of pressure-sensing.     

Preparation of Zn(Cd)O:Ga–SiO2 composite scintillating materials

Composite material consisting of highly luminescent Zn(Cd)O:Ga powder embedded in the silica matrix was prepared. It was found out that ZnO:Ga with less developed crystals (i.e. annealed at lower temperatures) is more prone to interact with the SiO₂ matrix and form zinc silicates, which in turn resulted in the decrease in the excitonic emission. Pre-annealing of the powders at temperatures above 600 °C prevented the interaction with the SiO₂ matrix. ZnO:Ga with well-developed crystals at such a high temperatures was not affected by the matrix and retained its properties, i.e. high radioluminescence intensity and ultrafast sub nanosecond photoluminescence decay. Introducing Cd into the ZnO lattice caused observable red shift in the excitonic luminescence, without negatively affecting the total intensity or the decay.     

Synthesis,Crystal Structure and Properties of Novel Composite Complex: [La(Nmp)4(H2o)4][HsiMo12O40]·2nmp·H2o

A new composite complex of [La(NMP)₄(H₂O)₄][HSiMo₁₂O₄₀]·2NMP·H₂O (NMP = N-methyl-2- pyrrolidone) was synthesized and characterized by IR, UV, ESR, TG-DTA and single crystal structural analysis. The water and organic ligands (NMP) coordinate directly with La(III) to form a dodecahedral complex and the SiMo₁₂O^4? ₄₀ anion is the counter ion. IR and X-ray analysis show that there is strong interaction between the polyoxometalate and organic donors. The complex is strongly photosensitive under irradiation with sunlight, resulting in a charge-transfer complex by oxidation of the N-methyl-2-pyrrolidone and reduction of the polyoxometalate. Low temperature ESR spectra indicate thermal electron delocalization among the Mo atoms in the title compound.     

硅橡胶包覆十八烷/聚(St-MMA)储能微胶囊复合材料制备及热性能

以十八烷/聚(苯乙烯-甲基丙烯酸甲酯)(P(St-MMA))微胶囊为相变材料,硅橡胶作为载体,制备了十八烷/P(St-MMA)/硅橡胶复合材料。研究了微胶囊的加入方式及加入量,硅橡胶包覆方法。通过红外光谱(IR)和扫描电镜(SEM)研究复合材料的结构和形貌。通过力学性能测试如拉伸强度、扯断伸长率,确定最佳的加工方法。通过热重分析法(TG)、差示扫描量热法(DSC)和储热性能对复合材料的热性能进行研究。结果表明,十八烷制成微胶囊加入到硅橡胶中,且微胶囊加入量是2份时,十八烷/P(St-MMA)微胶囊/硅橡胶的热稳定性热稳定性及力学性能较好。室温硅橡胶包覆微胶囊掺混固化法制备的复合材料的力学性能优于直接共混后热固化法和混炼涂抹后热固化法。十八烷/P(MMA-St)/硅橡胶复合材料的焓值为67.6J/g,储能效果好。     

Homogenization of parabolic problem with nonlinear transmission condition

In this paper, we investigate the periodic homogenization of nonlinear parabolic equation arising from heat exchange in composite material problems. This problem, defined in periodical domain, is nonlinear at the interface. This nonlinearity models the heat radiation on the interface, which constitutes the transmission boundary conditions, between the two components of the material. The main challenge is, first, to show the well-posedness of the microscopic problem using the topological degree of Leray–Schauder tools. Then, we apply the two scale convergence to identify the equivalent macroscopic model using homogenization techniques. Finally, in order to confirm the efficiency of the homogenization process, we present some numerical results obtained via finite element approximation.     

Influence of thermal and UV treatment on the polypropylene/graphite composite

Electrically conductive polypropylene/graphite (PP/graphite) composites were prepared via blending granulated PP with maleic anhydride grafted PP and natural graphite. Electrical conductivity of prepared samples containing either 65, 70, or 75 wt% of graphite was measured and the most conductive sample containing 75 wt% of graphite was exposed to UV irradiation for 1 and 24 h or thermally treated at 170 °C for 1 h. The influence of thermal and UV exposure on the structural and electrical changes in such treated samples was studied. Local current measurements on the surface were made using scanning spreading resistance microscopy and morphology of the surface was studied by atomic force microscopy. X-ray diffraction analysis, infrared and Raman spectroscopy were also used for the structural characterization. Properties of treated and untreated samples are compared and differences are discussed.     

GO/PVA nanocomposites with significantly enhanced mechanical properties through metalion coordination

In this study, a simple and efficient way is demonstrated to create strong interfacial interaction between graphene oxide(GO) filler and poly(vinyl alcohol)(PVA) matrix through metal ion coordination. The coordination bonding provides efficient load transfer during the tensile process, and enhances the mechanical properties of the nanocomposites significantly. After being coordinated with Cu(Ⅱ) ions, GO/PVA composites show much higher Young's moduli and yield stresses than pure PVA and noncoordinated GO/PVA. UV–vis and FTIR spectra are performed to confirm the successful coordination between GO and PVA. Ethylene diamine tetraacetic acid disodium salt(EDTA-2 Na) is used to confirm the important role of coordination in enhancing the composites. This research provides a new approach to manufacture polymer-matrix nanocomposites with significantly improved mechanical performances.