Effect of filler geometry on interfacial friction damping in polymer nanocomposites

Single-walled carbon nanotube polycarbonate and C60 polycarbonate nanocomposites were fabricated using a solution mixing method. The composite loss modulus was characterized by application of dynamic (sinusoidal) load to the nanocomposite and the pure polymer samples. For a loading of 1 weight %, the single-walled nanotube fillers generated more than a 250% increase in loss modulus compared to the baseline (pure) polycarbonate. Even though the surface area to volume ratio and surface chemistry of C60 is similar to that for nanotubes, we report no significant increase in the energy dissipation for the 1% weight C60 nanoparticle composite compared to the pure polymer. We explain these observations by comparing qualitatively, the active sliding area (considering both normal and shear stresses) for a representative volume element of the nanotube and the nanoparticle composites. These results highlight the important role played by the filler geometry in controlling energy dissipation in nanocomposite materials.     

聚合物/石墨导电纳米复合材料研究进展

石墨是近几年国内外研究的热点无机层状材料之一,它与聚合物有效复合形成的纳米复合材料是一类具有广阔应用前景的新型材料。从石墨的应用形式、聚合物基体的种类、复合材料的制备方法几个方面概述了聚合物/石墨导电纳米复合材料的研究进展及其发展趋势。     

The effect of filler particle size on the antibacterial properties of compounded polymer/silver fibers

Antibacterial activity has become a significant property of textiles used in applications such as medicine, clothing, and household products. In this study, we compounded polypropylene with either micro- or nano-sized silver powders. These polypropylene/silver compounds were prepared by direct melt-compounding using a conventional twin-screw mixer. We analyzed the characteristics of the compounds using wide-angle X-ray diffractometry (WAXS), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). The DSC and WAXS results indicated that the crystallinity of the polypropylene component decreased slightly when compared with that of the pure polymer. The SEM micrographs indicated that the silver particles had good dispersibility in the matrix. We measured the mechanical properties of these materials using a universal tensile tester and evaluated the antibacterial activities of these compounds by performing quantitative antibacterial tests using the AATCC-100 test method. From these evaluations of antibacterial activity, we conclude that the compounds incorporating the silver nanoparticles exhibited superior antibacterial activity relative to the samples containing micron-sized particles.     

A molecular dynamics simulation study to investigate the effect of filler size on elastic properties of polymer nanocomposites

The influence of filler size on elastic properties of nanoparticle reinforced polymer composites is investigated using molecular dynamics (MD) simulations. Molecular models for a system of nanocomposites are developed by embedding a fullerene bucky-ball of various sizes into an amorphous polyethylene matrix. In all cases, bucky-balls are modeled as non-deformable solid inclusions and infused in the matrix with a fixed volume fraction. The interaction between polymer and the nanoparticle is prescribed by the Lennard-Jones non-bonded potential. The mechanical properties for neat polymer and nanocomposites are evaluated by simulating a series of unidirectional and hydrostatic tests, both in tension and compression. Simulation results show that the elastic properties of nanocomposites are significantly enhanced with the reduction of bucky-ball size. An examination at the atomic level reveals that densification of polymer matrix near the nanoparticle as well as the filler-matrix interaction energy play the major role in completing the size effect.     

碳纳米管增强聚合物复合材料的研究进展

论述了碳纳米管/聚合物纳米复合材料的各种制备方法和最新进展。详细讨论了碳纳米管/聚合物纳米复合材料的结构和性能,并对今后的研究方向进行了展望。     

高分子导电复合材料的颗粒级配技术研究进展

本文重点介绍了复合材料尤其是碳系高分子导电复合材料中的颗粒级配技术的研究现状和进展,评述了级配方式对复合材料力学加工性能及导电性能的影响.同时指出多元颗粒的多级配是未来制备力学加工性能与导电性能兼优的碳系导电复合高分子材料的重要方向.     

Quantitative study of the dispersion degree in carbon nanofiber/polymer and carbon nanotube/polymer nanocomposites

Quantitative measurements of the filler dispersion degree of carbon nanofiber (CNF) and nanotube (CNT) reinforced polymer nanocomposites have been made by transmission electron microscopy. Samples were prepared by either high-shear mixing or twin-screw extrusion processing. It was found that the filler dispersion degree was largely influenced by the filler size. As the filler dimension became smaller, the dispersion parameter D_0.1 largely decreased as quantified, which demonstrated the challenges associated with improving the dispersion of smaller fillers. This work provided a method to quantitatively compare the dispersion degrees of CNF/CNT polymer nanocomposites.     

Porous polymer/hydroxyapatite scaffolds: characterization and biocompatibility investigations

Poly-lactic-glycolic acid (PLGA) has been widely used as a scaffold material for bone tissue engineering applications. 3D sponge-like porous scaffolds have previously been generated through a solvent casting and salt leaching technique. In this study, polymer–ceramic composite scaffolds were created by immersing PLGA scaffolds in simulated body fluid, leading to the formation of a hydroxyapatite (HAP) coating. The presence of a HAP layer was confirmed using scanning electron microscopy, energy dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy in attenuated total reflection mode. HAP-coated PLGA scaffolds were tested for their biocompatibility in vitro using human osteoblast cell cultures. Biocompatibility was assessed by standard tests for cell proliferation (MTT, WST), as well as fluorescence microscopy after standard cell vitality staining procedures. It was shown that PLGA–HAP composites support osteoblast growth and vitality, paving the way for applications as bone tissue engineering scaffolds.     

Influence of filler waviness and aspect ratio on the percolation threshold of carbon nanomaterials reinforced polymer nanocomposites

Adding a small amount of conductive high aspect one-dimensional nanomaterials such as carbon nanotubes and carbon nanofibers to the initially non-conductive polymeric matrix can induce an insulator to conductor transition which has both scientific merit and application importance. The critical fiber concentration necessary for this transition is called the percolation threshold, which is determined by the filler shape and size. This study investigates the filler waviness effect on the critical behavior of composite conductivity, since the high aspect ratio fillers in actual composites are often bent and entangled instead of being straight. Individual filler was modeled by a linked three straight-segment components with three-dimensional (3D) bending characteristics. In addition, 3D Monte Carlo method has been used to simulate the random distribution of the fillers. Statistical analyses of the fiber networks reveal waviness influence on the percolation threshold in terms of the average contacts per fiber with other fibers. The critical number of average contacts per fiber (B _c) for percolation strongly depends on the waviness and deviates substantially from identity for straight fillers. The study demonstrates that the semi-analytic excluded volume theory cannot be used to predict the percolation threshold until the correct B _c value is determined.     

石墨/聚合物纳米复合材料研究新进展

综述了最近3年国内外石墨/聚合物纳米复合材料的研究进展,阐述了石墨纳米薄片的制备方法,石墨的表面改性以及各种石墨/聚合物复合材料在电学、热学和摩擦学等领域中的性能特点。指出了石墨在制备功能聚合物纳米复合材料中的重要应用价值。     

Review on polymer/graphite nanoplatelet nanocomposites

Graphite nanoplatelets (GNPs) are a type of graphitic nanofillers composed of stacked 2D graphene sheets, having outstanding electrical, thermal, and mechanical properties. Furthermore, owing to the abundance of naturally existing graphite as the source material for GNPs, it is considered an ideal reinforcing component to modify the properties of polymers. The 2D confinement of GNPs to the polymer matrix and the high surface area make the GNP a distinctive nanofiller, showing superiorities in modification of most properties, compared with other carbon nanofillers. This review will summarize the development of polymer/GNP nanocomposites in recent years, including the fabrication of GNPs and its nanocomposites, processing issues, viscoelastic properties, mechanical properties, electrical and dielectric properties, thermal conductivity and thermal stability. The discussion of reinforcing effect will be based on dispersion, particle geometry, concentrations, as well as the 2D structures and exfoliation of GNPs. The synergy of GNPs with other types of carbon nanofillers used as hybrid reinforcing systems shows great potential and could significantly broaden the application of GNPs. The relevant research will also be included in this review.     

Influence of filler/matrix interactions on resin/hardener stoichiometry,molecular dynamics,and particle dispersion of silicon nitride/epoxy nanocomposites

The addition of nanofillers can have a significant influence on the resin stoichiometry of thermosetting polymer systems. Based on differential scanning calorimetry (DSC) results, it is estimated that the inclusion of 2 and 5 wt% of silicon nitride nanofiller displaces the resin/hardener stoichiometry of an epoxy/amine network by 6.5 and 18%, respectively. Dielectric spectroscopy results confirm the above findings, in that the spectra of the nanocomposite samples were found to be equivalent to the spectra of unfilled samples when the above stoichiometric effect was taken into account. Therefore, this study provides clear evidence that the presence of a nanofiller can directly and significantly affect the curing process of an epoxy network. Consequently, this should always be considered when introducing nanofillers into thermosetting matrices. These results indicate the presence of covalent bonding between the nanoparticles and the surrounding polymer and, therefore, provide an opportunity to explore the influence of this bonding on the molecular dynamics of the polymer layer around the particles. However, the obtained DSC and dielectric spectroscopy results suggest that, in the system considered here, either the covalent bonding does not have an appreciable influence on the segmental dynamics of the polymer, as revealed by these techniques, or that the thickness of the affected layer is less than 1 nm and therefore too small to be distinguished from experimental uncertainties.     

The effect of multi-walled carbon nanotubes/hydroxyapatite nanocomposites on biocompatibility

In the present study, multi-walled carbon nanotubes/hydroxyapatite (MWCNTs/HA) nanocomposites with various MWCNT contents were manufactured by sol-gel processing. The MWCNTs/HA powder was characterized using field-emission scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Raman analysis. The results show that the MWCNTs were fully covered with HA nanoparticles and help forming the crystallized hydroxyapatite. In addition, in vitro tests highlighted the excellent biocompatibility of the MWCNTs/HA composite.     

A molecular dynamics study on the interfacial properties of carbene-functionalized graphene/polymer nanocomposites

International Journal of Mechanics and Materials in Design - Atomic decoration of nanofillers, e.g. graphene sheets (GRs), is of extreme importance in their adequate dispersion into the matrices...     

Finestructures study of the diamond/titanium interface by transmission electron microscopy

It is well known that a TiC layer can be formed and should act as a buffer layer in diamond films deposited on Ti alloy. Through our cross-sectional investigation in HRTEM, a thin layer (20–30 nm) was first identified between the outermost diamond film and the inner reactive TiC layer adjacent to the substrate. This layer consists of numerous crystalline nanoparticles with grain sizes of 5–20 nm. Through electron nanodiffraction patterns combined with EDS and EELS analysis, these nanoparticles can be identified as a TiC_1−xO_x phase with a similar structure to cubic TiC. Besides, C atoms and O atoms in TiC_1−xO_x randomly occupy the vacancies of C in TiC. The thickness of this TiC_1−xO_x layer does not change significantly with increasing deposition time, and the diamond phase directly nucleates and grows on it.     

Effect of grafted polymer species on particle monolayer structure at the air-water interface

We have studied poly(methyl methacrylate)-grafted(PMMA) particle monolayer systems at the air-water interface. In previous papers, we reported that PMMA chains grafted from particles (silica particle and polystyrene latex) were extended on water surfaces. Through observing deposited particle monolayers on substrates using SEM, we have confirmed that PMMA of large molecular weights were either dispersed or arrayed in structure with long inter-particle distances approximately 500 nm. In contrast, low molecular weight PMMA were observed to aggregate upon deposition. We speculated that the difference in morphology in deposited particle monolayers would be attributed to the affinity between the grafted polymer and the substrate. To examine the effect of this affinity three new polymer-grafted silica particles were synthesized with a fairly high graft density of about 0.14 approximately 0.43 nm(-2). As well as PMMA-grafted silica particles (SiO2-PMMA), poly(2-hydroxyethyl methacrylate) and poly(t-butyl methacrylate)--grafted silica particles (SiO2-PHEMA and SiO2-PtBuMA) were also prepared and subjected to pi-A isotherm measurements and SEM observations. These pi-A isotherms indicated that polymer-grafted silica formed monolayer at the air-water interface, and the onset area of increasing surface pressure suggests that the polymer chains are extended on a water surface. However, the morphology of the deposited monolayer is highly dependent on polymer species: SiO2-PHEMA showed that the dispersed particle monolayer structure was independent of grafted molecular weight while SiO2-tBuMA showed an aggregated structure that was also independent of grafted moleculer weight. SiO2-PMMA showed intermediate tendencies: dispersed structure was observed with high grafted molecular weight and aggregated structure was observed with low grafted molecule weight. The morphology on glass substrate would be explaiened by hydrophilic interaction between grafted polymer and hydrophilic glass substrate.     

Effect of interface modification on PMMA/graphene nanocomposites

Graphene platelets (GnPs) were surface modified with a long-chain surfactant B200, and then compounded with polymethyl methacrylate (PMMA). B200 provided an anchor into GnPs and a bridge into the matrix, thus creating molecular entanglement between matrix and GnPs. The interface modification promoted the dispersion of GnPs, as no aggregates of GnPs were observed on the fracture surface of the modified composites, in sharp contrast with the unmodified composites. Although GnPs formed clusters in the matrix, bilayer graphene was readily observed under TEM in randomly selected regions; it showed high structural integrity under diffraction pattern. The addition of 2.7 vol% m-GnPs produced 32.8 % improvement in the flexural modulus of PMMA as compared to 9.0 % by unmodified GnPs. At 1.1 vol%, the interface-modified composite showed a 19.6 % improvement in the absorption resistance to ethanol, in comparison with 3.8 % for the unmodified composites. The addition of 2.7 vol% m-GnPs improved fracture toughness of PMMA by 79.2 %, while GnPs enhanced it by 23.9 %.     

Theoretical study of charge-induced defects at metal/polymer interface

Conducting polymers have attracted much attention concerning the possibility of their use as active components of electronic and optoelectronic devices. We use a molecular dynamics method with semi-empirical quantum chemistry at CNDO (complete Neglect of differential overlap) level to study the chemical interactions between aluminium atoms and trans-polyacetylene during the interface formation. Our results suggest that aluminium dimer (Al₂) bound to a polymer chain is energetically more favourable than the adsorption of isolated aluminium atoms. In both cases, the compound formation is accompanied by charge transfer between metal and polymer. As a result charge rearrangement among the polyacetylene atoms is induced. We shall describe the charge-induced structural relaxation of the trans-polyacetylene backbone which is accompanied by a local change in the electronic structure of the polymer, commonly called defects.     

Conducting polymer/clay nanocomposites and their applications

This review aims at reporting on interesting and potential aspects of conducting polymer/clay nanocomposites with regard to their preparation, characteristics and engineering applications. Various conducting polymers such as polyaniline, polypyrrole and copolyaniline are introduced and three different preparation methods of synthesizing conducting polymer/clay nanocomposites are being emphasized. Morphological features, structure characteristics and thermal degradation behavior are explained based on SEM/TEM images, XRD pattern analyses and TGA/DSC graphs, respectively. Attentions are also being paid on conductive/magnetic performances as well as two potential applications in anti-corrosion coating and electrorheological (ER) fluids.     

Synthesis and characterization of FeNi/polymer nanocomposites

Alloyed spherical FeNi-polymer nanocomposites were prepared via wet chemical method using hydrazine as a reducing agent and polymers (PVP and PEG) as reducing and stabilizing agent. Structural studies performed using XRD and TEM shows uniform dispersion of fine FeNi nanocrystallites in nanocomposite particles. The size and thermal stability of FeNi-polymer nanocomposite particles prepared under same reaction condition was found to be dependent on the type and the molecular weight of the polymer used. However, the magnetic properties of nanocomposite particles were not influenced by the polymers. The study highlights subtle differences in using polymers during the synthesis of alloyed nanocomposite particles.