Effectiveness of Maleic Anhydride Grafted EPDM Rubber (EPDM-g-MAH) as Compatibilizer in NR/Organoclay Nanocomposites Prepared by Melt Compounding

The effectiveness of maleic anhydride grafted ethylene propylene diene monomer rubber (EPDM-g-MAH) as an interfacial compatibilizer in enhancing the extent of interaction between natural rubber (NR) matrix and organoclay (OC) nanolayers, and also the eventually developed microstructure during a melt mixing process, has been evaluated as an alternative material to be used in place of commonly used epoxidized NR with 50 mol % epoxidation (ENR50). The latter usually weakens the processability of the final compound. The curing behavior, rheological, and dynamic mechanical properties of the prepared nanocomposites have been evaluated. Microstructural characterizations revealed better interfacial compatibilization by EPDM-g-MAH than ENR50, which is attributed to the lower polarity of the EPDM-g-MAH and hence more affinity for the NR matrix to be diffused onto the galleries of OC. This was confirmed with transmission electron microscopy (TEM) examination and higher elasticity exhibited by the unvulcanized NR/OC/EPDM-g-MAH nanocomposites in melt rheological measurements. Also, lower damping behavior was observed for the vulcanized NR/OC/EPDM-g-MAH samples. These imply intensified polymer–filler interfacial interaction and hence restricted viscous motions by the NR segments. Vulcanized NR/OC nanocomposites compatibilized with EPDM-g-MAH showed greater enhancements in tensile properties than the sample compatibilized with ENR50.     

Partial reduction of graphene oxide upon intercalation into exfoliated manganese thiophosphate

Abstract

We have prepared novel nanohybrid Li_2xMn_1?xPS₃/GO films consisting of graphene oxide (GO) and exfoliated MnPS₃ nanosheets via an easy mixing protocol at room temperature. These films were investigated by SEM and AFM, as well as XRD, Raman and XPS spectroscopies, obtaining information about the nature of the interaction between MnPS₃ and GO. In particular, the dark colour of the nanocomposite film and, more to the point, the analysis of (i) the C1s core level XPS spectra, (ii) the interlayer spacing obtained by XRD measurements and (iii) the increment in the intensity ratio I_D/I_G of the two bands typical of the carbon region of GO Raman spectra, suggest that a partial reduction of GO can be obtained right upon intercalation into Li_2xMn_1?xPS₃.     

石墨烯/银纳米复合材料的制备及其影响因素研究

以硝酸银、鳞片石墨为原料, 在强碱环境下, 制备得到石墨烯/银纳米复合材料, 采用X射线衍射、红外吸收光谱、透射电子显微镜、紫外可见分光光度计对所制备的石墨 烯/银纳米复合材料进行了表征.结果表明: 氧化石墨烯和银离子在强碱NaOH的作用下, 氧化石墨烯失去部分含氧官能团, 被部分还原为石墨烯(rGO), 银离子被还原为纳米银颗粒, 均匀分布在氧化石墨烯片层表面, 颗粒大小和分布受硝酸银用量、反应温度、NaOH的加入顺序及前驱物混合方式等因素影响, 在GO与Ag粒子质量比为 1:1.08时, 负载在石墨烯片层上的银纳米颗粒集中在12 nm左右. 关键词： 石墨烯/银纳米复合材料 强碱溶液     

Aromatic Polyimide/MWCNT Hybrid Nanocomposites: Structure,Dynamics, and Properties

Two series of hybrid polyimide (PI)/multiwalled carbon nanotube (MWCNT) nanocomposites were prepared including COOH-functionalized or pristine nanotubes, and their structure, morphology and dynamics/mechanical properties at 20°C–500°C were studied using WAXD (Wide-angle X-ray diffraction), AFM (Atomic force microscopy), TEM (transmission electron microscopy), DSC (Differential scanning calorimetry), DMA (Dynamic mechanical analysis), CRS (creep rate spectroscopy) techniques, and stress–strain testing. The impact of nanofiller loadings of 0.125, 0.25, 0.5, or 1 wt% relative to PI was evaluated. Specific changes in the matrix morphology and different quality of nanotube dispersion in the nanocomposites with amorphous and semicrystalline matrices were determined. The best nanotube dispersion was observed in the composites with 0.5 wt% MWCNT-COOH. A peculiar high temperature dynamics, different for amorphous, and semicrystalline matrices, was revealed in these nanocomposites. The most dramatic changes in high temperature dynamics and a pronounced dynamic heterogeneity as well as substantially enhanced mechanical properties at room temperature were revealed in the case of a semicrystalline PI matrix. The results were treated in terms of the synergistic impact of nanotubes and matrix crystallites on dynamics in the intercrystalline regions of PI (“combined constrained dynamics effect”) and the peculiar interfacial dynamics.     

Polypropylene Nanocomposites Based on Synthetic Organic-Soluble Ag Nanocrystals with Prominent β-nucleating Effect: Quiescent Crystallization and Melting Behavior

Differential scanning calorimetry, x-ray diffraction, and polarized optical microscopy were used to investigate the quiescent crystallization and melting behavior of isotactic polypropylene (iPP) nanocomposites based on synthetic organic-soluble Ag nanocrystals (NCs). The effects of Ag loading and crystallization temperature on the crystallization behavior and crystalline structure were studied. The results showed that the synthetic Ag NCs as a novel effective β-crystal nucleating agent for iPP could promote the overall crystallinity, decrease the size of spherulites, and induce the formation of large amounts of β-crystals in the nanocomposites under quiescent crystallization. The relative content of β-crystals significantly increased with increasing Ag loading, and slightly increased with decreasing crystallization temperature. The quiescent crystallization kinetics was analyzed using the Avrami model. The results showed that the iPP nanocomposites with added Ag NCs had higher crystallization rate constant (k) and lower crystallization half-times (t_1/2) as well as the Avrami exponent (n) than pure iPP, indicating that the presence of Ag NCs acted as heterogeneous nucleating sites and promoted the crystallization rate of iPP.     

Mechanical and Thermal Performance of High-Density Polyethylene/Alumina Nanocomposites

High-density polyethylene (HDPE) nanocomposites reinforced with pristine and vinyltrimethoxysilane (VTMS)-treated alumina nanoparticles of 2, 4, and 6 wt% were melt-compounded in a twin-screw extruder followed by injection molding. Their structure, thermal and mechanical behaviors were studied. Fourier transform infrared (FTIR) spectra showed that VTMS was successfully covalently grafted to the alumina nanoparticles. The X-ray diffraction (XRD) patterns indicated that the alumina nanoparticle additions broadened the characteristic peak width of HDPE, indicating that they reduced the crystallite size of HDPE. The heat deflection temperature and thermogravimetric analyses demonstrated that the dimensional and thermal stability of HDPE were enhanced markedly by adding pristine and silane-treated alumina nanoparticles. The alumina nanoparticle additions were also beneficial in enhancing Young's modulus and yield strength of HDPE. The reinforcing effect was particularly apparent in the silane-treated nanocomposites due to improved filler–matrix interactions.     

Thermal and Tensile Properties of Epoxy Nanocomposites Reinforced by Silane-functionalized Multiwalled Carbon Nanotubes

Epoxy nanocomposites with unmodified multiwalled carbon nanotubes (u-MWCNTs) and silanized multiwalled carbon nanotubes (si-MWCNTs) were prepared by a cast molding method. The effects of 3-aminopropyltriethoxysilane functionalization of MWCNTs on thermal, tensile, and morphological properties of the nanocomposites were examined. The nanocomposites were characterized by thermogravimetric analysis, dynamic mechanical thermal analysis, and tensile testing. The results showed that epoxy composites based on si-MWCNTs showed better thermal stability, glass transition temperature, and tensile properties than the composites based on u-MWCNTs. These results prove the effect of silane functionalization on the interfacial adhesion between epoxy and MWCNTs. This was further confirmed by morphology study of fractured surfaces of nanocomposites by field emission scanning electron microscopy.     

Micromechanical model for self-organized secondary phase oxide nanorod arrays in epitaxial YBa2Cu3O7−δ films

A micromechanical model based on the theory of elasticity has been developed to study the configuration of self-assembled secondary phase oxide nanostructures in high-temperature superconducting YBa₂Cu₃O_7?δ films. With the calculated equilibrium strain and elastic energy of the impurity doped film, a phase diagram of lattice mismatches vs. elastic constants of the dopant was obtained that predicts the energetically preferred orientation of secondary phase nanorods. The calculation of the nanorod orientation and the film lattice deformation has yielded excellent agreement with experimental measurements.     

Linear and nonlinear dielectric properties of nanocomposites based on the organic ferroelectric of diisopropylammonium bromide

ABSTRACT

The present work aims at investigating linear and nonlinear dielectric properties of nanocomposites based on diisopropylammonium bromide (C₆H₁₆NBr, DIPAB) embedded into Al₂O₃ films having honeycomb structure with pores of 100?nm in diameter, and into opal matrices with three-dimensional structure containing pores of 100 and 60?nm. The obtained results indicated the shift of Curie point toward lower temperatures for DIPAB in porous aluminum oxide and the appearance of two phase transitions, detected upon heating and cooling for DIPAB in opal matrices. In addition, a ferroelectric phase was found to form between these two phase transitions without significant change of Curie temperature.     

Growth and magnetic behavior of bismuth substituted yttrium iron garnet nanoparticles

Crystal growth and the magnetic properties of bismuth substituted yttrium iron garnet (Bi-YIG) nanoparticles were studied with particular focus on the bismuth composition dependence of the magnetic properties of the particles and the effects of annealing on the garnet phase formation. The Bi-YIG nanoparticles of 47–67 nm in size can be chemically synthesized when they are annealed at 650–850 °C. Both the lattice constant and the magnetization of the garnet nanoparticles linearly increase when the bismuth composition in the Bi-YIG particles increases. We have found that chemically synthesized nanoparticles transform from the amorphous to the garnet phase when annealed at temperatures below 650 °C, while the onset of magnetic moment of iron in the garnet nanoparticles is observed slightly above 650 °C. According to Mössbauer effect measurements, the hyperfine fields of ⁵⁷Fe at the tetrahedral and octahedral sites in the garnet are 39 and 48 T, respectively.