N-PMI/MMA/AN乳液共聚物的合成及热分析研究

通过乳液共聚合的方法合成了N－苯基马来酰亚胺（N－PMI）／甲基丙烯酸甲酯（MMA）丙烯腈（AN）三元共聚物,用DSC,TBA及TGA热分析方法对共聚物的热性能进行了对比表征,实验结果表明,TBA能 了地表征N－PMI对共聚物耐热性能的影响,从TGA结果看,加入N－PMI可以有效地提高材料的热分解温度。同时用GPC对共聚物的平均分子量及其分布进行了表征。     

聚合温度对丙烯腈/丙烯酸甲酯共聚物结构与性能的影响

在不同聚合温度下,以水相沉淀聚合法合成了丙烯腈与丙烯酸甲酯共聚物。采用差示扫描量热分析(DSC)、元素分析(EA)、核磁共振波谱分析(NMR)等方法对聚合物的组成和结构进行了表征。结果表明,不同的聚合温度对丙烯腈与丙烯酸甲酯共聚物的热力学行为、组成及序列长度产生一定的影响。相同的单体投料比,随着聚合温度的升高,共聚物中丙烯腈的摩尔含量降低,丙烯腈的数均序列长度减小。     

超声振荡和羟丙基甲基纤维素对短切纤维在精铸硅溶胶浆料中分散性能的影响

采用超声振动和加入羟丙基甲基纤维素(HPMC)对硅溶胶基体中的短切尼龙纤维进行分散,研究了不同超声功率作用和HPMC分散剂不同加入量对纤维在硅溶胶中分散效果的影响;观察了纤维在硅溶胶分散体系中的数码照片,测试了浆料的运动黏度,用纤维质量的变动系数和差异率评价纤维的分散性,并在扫描电镜下观测硅溶胶浆料中纤维的分布情况。结果表明:通过超声振荡和机械搅拌的协同作用,纤维在硅溶胶分散体系中的分散效果得到了明显提高,当超声功率为900W时,纤维分散较均匀;加入HPMC分散剂有效地改善了纤维的分散性,HPMC加入量在0.2%(质量分数,下同)~0.3%之间,纤维的分散效果最理想,当加入0.4%HPMC时,反而阻碍了纤维的分散。     

Effect of an organic compound (Methyl Red) interfacial layer on the calculation of characteristic parameters of an Al/Methyl Red/p-Si sandwich Schottky barrier diode

An Al/Methyl Red/p-Si sandwich Schottky barrier diode (SBD) has been fabricated by adding a solution of the organic compound Methyl Red in chloroform onto a p-Si substrate, and then evaporating the solvent. Current-voltage (I-V) measurements of the Al/Methyl Red/p-Si sandwich SBD have been carried out at room temperature and in the dark. The Al/Methyl Red/p-Si sandwich SBD demonstrated rectifying behavior. Barrier height (BH) and ideality factor values of 0.855 eV and 1.19, respectively, for this device have been determined from the forward-bias I-V characteristics. The Al/Methyl Red/p-Si sandwich SBD showed non-ideal I-V behavior with the value of ideality factor greater than unity. The energy distribution of the interface state density determined from I-V characteristics increases exponentially with bias from 3.68 × 10¹² cm^− 2 eV^− 1 at (0.81 − E_v) eV to 9.99 × 10¹³ cm^− 2 eV^− 1 at (0.69 − E_v) eV.     

苯乙烯-丙烯酸甲酯共聚物对聚苯乙烯/聚乳酸共混物力学性能和流变性能的影响

采用无皂乳液聚合法合成了苯乙烯-丙烯酸甲酯共聚物(PSMA)(n(St)∶n(MA)=75∶25),将PSMA与聚苯乙烯(PS)和聚乳酸(PLA)熔融共混制备了PSMA含量不同的PS/PLA共混物(m(PS)∶m(PLA)=1∶4),利用扫描电子显微镜、电子拉力机和转矩流变仪对共混物的相结构、力学性能以及流变行为进行了表征。结果表明,加入少量PSMA即能有效提高PLA与PS的相容性,减小PS/PLA共混物中分散相的相尺寸,提高PLA与PS两相间粘接作用;加入质量分数为0.5%的PSMA时,PS/PLA共混物的力学性能达到最佳;未加PSMA时,PS/PLA共混物在高剪切速率下剪切变稀显著,甚至低于纯PS,加入PSMA后,在高剪切速率下的剪切变稀程度与纯PLA相当。     

阴离子本体开环聚合反应挤出合成聚三氟丙基甲基硅氧烷

以同向紧啮合双螺杆挤出机为反应器,硅醇钠/乙酸乙酯(EA)为引发体系,通过三氟丙基甲基环三硅氧烷(F3)阴离子本体开环聚合,制备了聚三氟丙基甲基硅氧烷(PMTFPS)。采用红外光谱(FT-IR),核磁共振(1H-NMR)和凝胶渗透色谱(GPC)确认了聚合物的结构与分子量,用电离飞行时间质谱分析了副产物的组成。研究表明,提高反应温度和EA用量可使反应平衡点提前到达。而螺杆转速对反应的主要影响在于改变聚合反应时间。因此,控制适当反应条件,使反应在平衡点到来时间之前终止,可得到高分子量以及高收率的PMTFPS。所得产物的数均分子量为2.41×105,分子量分散指数为1.12,产率为90.5%。     

溶剂对介孔二氧化钛结构及光催化活性的影响

在室温下采用不同溶剂直接合成出介孔TiO2，分别用场发射透射电镜（HRTEM）、透射电镜（TEM），X射线粉末衍射（XRD）和BET比表面测定等技术对TiO2进行了表征。结果表明：在该实验条件下能获得高比表面的介孔TiO2，溶剂的极性对孔结构有一定的影响，同时对甲基橙的光催化降解活性有较大的影响。     

Effect of thickness on the structural, electrical and optical properties of ZnO films

A series of ZnO films of different thickness have been deposited on glass substrates using sol-gel technique by varying the number of spin coatings and the effect of film thickness on the structural, electrical and optical properties have been investigated. The XRD results indicate that the full width at half maximum (FWHM) of the (0 0 2) diffraction peak and the strain along c-axis are decreased as the film is grown up to a thickness of 300 nm. Above 300 nm, the strain again becomes appreciable. The surface morphology shows that the grains become more uniform and bigger in size as the film thickness increases. Electrical result shows that although ZnO film with thickness of around 260 nm has the highest resistivity but is better for current conduction. The excitonic nature in the absorption spectrum becomes prominent for a film with thickness of around 260 nm. The band gap increases and then decreases as the film grows thicker.     

Effect of a ZnSe buffer layer on the surface, structural, and optical properties of the ZnTe/ZnSe/GaAs heterostructures

Lattice-mismatched ZnTe epilayers on GaAs (1 0 0) substrates with and without ZnSe buffer layers were grown by using molecular beam epitaxy. AFM, XRD, and TEM measurements were performed to investigate the surface and structural properties of the ZnTe thin films. Photoluminescence, Raman scattering, and TEM measurements showed that the crystallinity of a ZnTe epilayer grown on a GaAs substrate was remarkably improved by using a ZnSe buffer layer. Photoreflectance measurements showed that the strain of the ZnTe layer with the ZnSe buffer layer was smaller than that without the ZnSe buffer layer. These results indicate that ZnTe epitaxial films grown on GaAs substrates with ZnSe buffer layers hold promise for potential applications in optoelectronic devices operating in the blue-green spectral region.     

Effect of heat treatment on the properties of Metglas foils, and laminated magnetoelectric composites made thereof

Annealing of magnetostrictive Metglas foils, subsequently incorporated into laminated Metglas/Pb(Zr, Ti)O₃ magnetoelectric (ME) composites, is shown to result in improved magnetic properties, as well as ME coefficients. Annealing of the foils at 350 °C resulted in partial crystallization, without oxidation or magnetic cluster formation that would reduce the magnetization. Laminate composites made with these annealed Metglas foils had improved ME coefficients.     

Effect of the fluoride additives on the oxidation of AlN

The oxidation of AlN powder added by the fluorides at temperatures below 700°C in air was discovered in this study. The obvious onset of oxidation of AlN with cryolite and YF₃ additions is below 700°C with the product of α-Al₂O₃ phase, which usually occurs in single AlN powder above 1100°C. The changes on the weight and the FTIR spectra of the AlN powder fired at temperatures lower than 700°C show that cryolite and YF₃ greatly promote the oxidation of AlN powder at these temperatures. Different from the action of cryolite and YF₃ powder, CaF₂ has no obvious effect on the oxidation of AlN. A possible oxidation process, in part corroborated by FTIR and XRF, was proposed to explain the results in the experiments. The oxidation kinetics of AlN in the presence of cryolite were also discussed at the temperatures ranging from 550 to 700°C from the data of the weight gains in this region. The result shows that the oxidation follows a linear law, which implies a reaction rate-controlled process. The considerably low activation energy of 67 kJ mol⁻¹, which is associated with the quick oxidation and the formation of α-Al₂O₃ at temperatures below 700°C, was determined from the slope of the line fit.     

Effect of shearing on the orientation, crystallization and mechanical properties of HDPE/attapulgite nanocomposites

High density polyethylene (HDPE)/attapulgite (AT) nanocomposites, prepared by conventional injection molding (CIM) and dynamic packing injection molding (DPIM), were investigated with focus on AT-induced crystallization and orientation under shear. Infrared spectroscopy (FTIR) analysis showed there is no special chemical interaction between HDPE and AT, but shear induced significant changes on the material structure and properties. Differential scanning calorimetry (DSC) analysis showed strong nucleation effect by AT especially under shear. And more, shear will induce much better dispersion of AT in the DPIM sample vs. CIM. AT nanorods and lamellae of HDPE are more organized in the DPIM sample while there is only random distribution in the CIM sample. Most AT nanorods embed in the HDPE lamellae and form a brush-like hybrid structure due to shear. The shear-induced orientation will be enhanced with higher AT loading. The mechanical performance of the composites was significantly improved via DPIM.     

Effect of fiber,matrix and interface properties on the in-plane shear deformation of carbon-fiber reinforced composites

The effect of fiber, matrix and interface properties on the in-plane shear response of carbon-fiber reinforced epoxy laminates was studied by means of a combination of experiments and numerical simulations. Two cross-ply laminates with the same epoxy matrix and different carbon fibers (high-strength and high-modulus) were tested in shear until failure according to ASTM standard D7078, and the progressive development of damage was assessed by optical microscopy in samples tested up to different strains. The composite behavior was also simulated through computational micromechanics, which was able to account for the effect of the constituent properties (fiber, matrix and interface) on the macroscopic shear response. The influence of matrix, fiber and interface properties on each region and on the overall composite behavior was assessed from the experimental results and the numerical simulations. After the initial elastic region, the shear behavior presented two different regions, the first one controlled by matrix yielding and the second one by the elastic deformation of the fibers. It was found that in-plane shear behavior of cross-ply laminates was controlled by the matrix yield strength and the interface strength and was independent of the fiber properties.     

Effect of ZnO addition on the sintering and electrical properties of (Mn,W)-doped PZT-PMS-PZN ceramics

The effect of ZnO addition on the phase structure, microstructure and dielectric and piezoelectric properties of 0.2 wt.% MnO₂ and 0.6 wt.% WO₃-doped Pb(Zr_0.52Ti_0.48)O₃-Pb(Mn_1/3Sb_2/3)O₃-Pb(Zn_1/3Nb_2/3)O₃ (PZT-PMS-PZN) ceramics was investigated. X-ray diffraction shows that the phase structure of ceramics is transformed from rhombohedral to tetragonal with the increasing of ZnO addition. The bulk density significantly increases when ZnO is added and then it slightly decreases for ZnO addition above 0.2 wt.%. SEM micrographs show the grains of ceramics are uniform and well developed by adding 0.1 wt.% ZnO. The Curie temperature (T_c) of 270 °C is obtained at the 0.1 wt.% ZnO addition. Mechanical quality factor (Q_m), electromechanical coupling factor (K_p) and piezoelectric constant (d₃₃) increase firstly, and then decrease with the increasing of ZnO addition, while dielectric loss tan δ drops all the time. The Q_m, K_p, d₃₃, tan δ and T_c of the ceramics show the optimum values of 1899, 0.55, 300 (pC/N), 0.0063 and 270 °C, respectively, at the lower sintering temperature of 1120 °C and with 0.1 wt.% ZnO addition.     

h-BN用量对h-BN/MVQ导热绝缘复合材料性能的影响

以甲基乙烯基硅橡胶(MVQ)为基体,偶联剂改性后的六方片状氮化硼(h-BN)为填料,使用密炼机密炼,双辊开炼机辊压混合,模压成型制备了导热绝缘复合材料。运用橡胶加工分析仪、扫描电子显微镜、导热分析仪及阻抗分析仪研究了h-BN用量对MVQ的动态模量、硫化特性、断面微观形貌、导热性能、电绝缘性能的影响。实验结果表明,随着h-BN用量的增加,MVQ的焦烧时间及正硫化时间缩短,理论硫化时间延长,热导率与介电常数上升,当h-BN填充量为50 phr时,h-BN/MVQ复合材料的热导率达到1.13 W/(m·K),介电常数为3.87。     

Effect of graphene oxide on the physical,mechanical and thermo-mechanical properties of neoprene and chlorosulfonated polyethylene vulcanizates

The present research work demonstrated the effect of graphene oxide (GO) on the physical, mechanical, thermo-mechanical etc., properties of neoprene (CR) and chlorosulfonated polyethylene (CSPE) vulcanizates. CR and CSPE based nanocomposites were prepared by both solution intercalation and melt intercalation methods. The changes obtained in the morphology, cure characteristics, mechanical, thermal, thermo-mechanical properties of the rubber nanocomposites have been widely investigated. X-ray diffraction analysis (XRD) and transmission electron microscopic (TEM) analysis of the samples revealed partial exfoliated structure of GO containing rubber composites. Mechanical, thermal, cure and thermo-mechanical properties of the elastomeric nanocomposites were improved compared to the neat rubbers.     

Effect of thermo-hygrometric exposure on frp,natural stone and their adhesive interface

As well known, the performance of Fiber Reinforced Polymer (FRP) materials as external strengthening technique is strongly dependent on the bond behavior between FRP and substrate. Several experimental studies have been performed on this topic, however limited attention has still focused on the bond durability. In this paper, the effect of a thermo-hygrometric environment on the interface behavior FRP-calcareous natural stones isinvestigated. Each utilized materials (natural stone, adhesive, FRP sheets) was firstly exposed to the same thermo-hygrometric atmosphere; a relevant decay of mechanical properties has been found for the analyzed substrates (Lecce stone and Neapolitan tuff) while a negligible influence of the exposure has been observed for the composite reinforcements (CFRP and GFRP). The results regarding the variation of mechanical properties of the resins evidenced that the effect of the performed exposure is strictly correlated to the specific materials properties: a relevant degradation or even an improvement of mechanical performances has been,in fact, registered. The bond strength and the kind of failure were both analyzed as a function of the treatment used, as well as the strain and stress distribution at the interface. The kind of failure changed in some cases when passing from unconditioned to conditioned specimens; the bond strength, the maximum bond stress and the interface stiffness were affected by the treatment, manly depending on the adhesive resin deterioration. Finally, on the basis of the provisions given by the CNR-DT 200 R1/2013 document, the possibility of defining design relationships, able to take into account also durability aspects, is discussed.     

Effect of magnetic nanoparticles on the properties of magnetic rubber

A new kind of magnetic rubber was prepared through conventional rubber mixing techniques on a two-roll mill, in which the magnetic filler was Fe₃O₄ nanoparticles and was surface modified. The effect of Fe₃O₄ nanoparticles’ content on the mechanical and magnetic properties of nature rubber was further investigated. The obtained results of six different compositions for nature rubber with 0, 5, 10, 15, 20 and 25 phr of Fe₃O₄ nanoparticles were compared. It was found that the magnetic rubber has higher magnetic properties and tensile strength, comparing with unfilled nature rubber. The result suggests that when the magnetic filler is nanoparticles and surface modified, the mechanical and magnetic properties of the rubber can be synchronously improved, which is difficult to be observed in previous work.     

Effect of nanotube geometry on the elastic properties of nanocomposites

Many analytical models replace carbon nanotubes with “effective fibers” to bridge the gap between the nano and micro-scales and allow for the calculation of the elastic properties of nanocomposites using micromechanics. Although curvature of nanotubes can have a direct impact on these properties, it is typically ignored. In this work, the nanotube geometry in 3D is included in the calculation of the elastic properties of a modified effective fiber. The strain energy of the nanotube and the effective fiber are calculated using Castligiano’s theorem and constraints imposed by the matrix on the deformation are taken into consideration. Model results are compared to results from archived literature, and a reasonable agreement is observed. Results show that the effect of nanotube curvature on reducing the modulus of the effective fiber is not limited to in-plane curvature but also to curvature in 3D. The impact of the nanotube curvature on the elastic properties of nanocomposites is studied utilizing the modified fiber model and the approach developed by Mori–Tanaka. Analytical results show that for a low weight fraction of nanotubes the effect of curvature seems to be minor and as the weight fraction increases, the effect of nanotube curvature becomes critical.     

Effect of coupling agent and nanoclay on properties of HDPE,LDPE, PP,PVC blend and Phargamites karka nanocomposite

High density polyethylene (HDPE), low density polyethylene (LDPE), polypropylene (PP) and poly(vinyl chloride) (PVC) were solution blended by using a mixture of xylene and tetrahydrofuran as solvent and polyethylene-co-glycidyl methacrylate (PE-co-GMA) as compatibilizer. The minimum ratio of solvents to obtain a homogenous solution was optimised. Wood polymer composites (WPC) were prepared by using solution blended polymer, wood flour and nanoclay. X-ray diffraction studies of WPC treated with 1 and 3 phr nanoclay showed higher exfoliation compared to WPC treated with 5 phr nanoclay. TEM study also supported the above findings. FTIR studies indicated an interaction between wood, PE-co-GMA and clay. SEM study indicated an increase in miscibility among polymers due to addition of PE-co-GMA as compatibilizer. Thermal stability improved on addition of clay to the WPC. WPC treated with 3 phr clay showed highest mechanical properties. Hardness and water absorption were improved significantly with the addition of nanoclay to wood/polymer composite.