Magnetic nanostructured polymer composites

Magnetic polymer composites filled with microparticles of the nanocrystalline 5BDSR alloy have been studied. Measurements have been performed mainly by the ferromagnetic resonance method complemented by other spectroscopic methods. A quasi-stepwise structure of spectra near the direction of the magnetic field perpendicular to the nanocomposite plate has been found. It has been shown that incorporation of nanoparticles of technical carbon into the composite leads to a nonmonotonic concentrational dependence of the broadening of spectral lines, which is caused by spatial variations in the perpendicular magnetic anisotropy. The ferromagnetic resonance spectrum has been processed by taking into account the scatter of the magnetic anisotropy and demagnetizing factors.     

Fractal and structural aspects of adhesion in particulate-filled polymer composites

Two types of composites based on poly(hydroxy ether) and graphite with various amounts of a filler have been investigated by various methods. The methods have been used to estimate the characteristics of adhesion and interfacial layer, including its thickness and tensile strength and interdependence between these values and adhesion. The results are treated on the basis of the theory of irreversible aggregation, cluster theory of the polymer structure and fractal analysis. It is established that all important characteristics of adhesion, interfacial layer and mechanical properties are interconnected with the difference between fractal dimensions of the surface of the aggregates of filler particles and of a polymer matrix, whose structure is distorted under the influence of the filler surface.     

Predicting the mechanical properties of spider silk as a model nanostructured polymer

Spider silk is attractive because it is strong and tough. Moreover, an enormous range of mechanical properties can be achieved with only small changes in chemical structure. Our research shows that the full range of thermo-mechanical properties of silk fibres can be predicted from mean field theory for polymers in terms of chemical composition and the degree of order in the polymer structure. Thus, we can demonstrate an inherent simplicity at a macromolecular level in the design principles of natural materials. This surprising observation allows in depth comparison of natural with man-made materials.     

Enhanced thermal–mechanical properties of polymer composites with hybrid boron nitride nanofillers

The present work focuses on the investigation of the thermal–mechanical properties of the epoxy composites with hybrid boron nitride nanotubes (BNNTs) and boron nitride nanosheets (BNNSs). The stable dispersions of BNNTs–BNNSs were achieved by a noncovalent functionalization with pyrene carboxylic acid. The resulting epoxy/BNNTs–BNNSs composites exhibited homogeneously dispersed BNNTs–BNNSs and a strong filler–matrix interface interaction. The composites showed a 95 % increase in thermal conductivity and a 57 % improvement in Young’s modulus by addition of only 1 vol. % BNNTs–BNNSs. Meanwhile, the composites also retained a high electrical resistance of pure epoxy. Our study thus shows the potential for hybrid BNNTs–BNNSs to be successfully used as the nanofillers of polymer composites for applications in electrically insulating thermal interface materials.     

AlN/BN纳米结构多层膜微结构及力学性能

用射频磁控溅射法制备了AlN,BN单层膜及AlN/BN纳米多层膜.采用X射线衍射仪、高分辨率透射电子显微镜和纳米压痕仪对薄膜结构进行表征.分析表明：单层膜AlN为w-AlN结构,BN为非晶相.AlN/BN多层膜中BN的结构与BN层厚有关.当BN层厚小于0.55nm时,由于AlN层模板的作用,BN发生了外延生长,BN与AlN的结构相同;当BN层厚大于0.74nm时,BN为非晶.AlN/BN多层膜的硬度也与BN层的厚度有关.当BN层厚为1—2个分子层时,AlN/BN多层膜具有超硬效应;当BN层厚增加到0.74 关键词： AlN/BN多层膜 BN结构 超硬效应     

How to define a nanocomposite by the example of polymer/organoclay nanostructured composites

Physics of the Solid State - Introducing the filler nanoparticles into a polymer matrix is shown to not necessarily favor the formation of a true nanomaterial (nanocomposite). For this, a certain...     

Interfacial structure and mechanical properties of MgLi matrix composites

The study on interfacial structure and tensile properties of MgLi matrix composites. The results showed that there was a clear interface between the MgLi matrix and SiC whiskers. Calculation of thermodynamics confirmed that the clear interface between the matrix and SiC whiskers may contribute to the low reactionary potential or the low reactionary dynamics. However, some SiC whiskers were attacked. As a result, SiC whiskers connected with matrix in {111} and formed 70.5° or 109.5° stages on the whiskers surface in {111} face. The reason was the lower interfacial energy of {111} face. Tensile test confirmed that the SiC_w /MgLiAl composites showed higher tensile strength and higher modulus compared with MgLi matrix. Moreover, the specific strength and specific modulus were also increased obviously.     

Formulation and mechanical properties of emulsion-based model polymer foams

We produce cellular material based on the formulation of model emulsions whose drop size and composition may be continuously tuned. The obtained solid foams are characterized by narrow cell and pore size distributions in direct relation with the emulsion structure. The mechanical properties are examined, by varying independently the cell size and the foam density, and compared to theoretical predictions. Surprisingly, at constant density, Young’s modulus depends on the cell size. We believe that this observation results from the heterogeneous nature of the solid material constituting the cell walls and propose a mean-field approach that allows describing the experimental data. We discuss the possible origin of the heterogeneity and suggest that the presence of an excess of surfactant close to the interface results in a softer polymer layer near the surface and a harder layer in the bulk.     

Mechanical properties of sisal fibre-reinforced polymer composites: a review

There has been a growing interest in the utilization of sisal fibres as reinforcement in the production of polymeric composite materials. Natural fibres have gained recognition as reinforcements in fibre polymer–matrix composites because of their mechanical properties and environmental friendliness. The mechanical properties of sisal fibre-reinforced polymer composites have been studied by many researchers and a few of them are discussed in this article. Various fibre treatments, which are carried out in order to improve adhesion, leading to improved mechanical properties, are also discussed in this review paper. This review also focuses on the influence of fibre content and fabrication methods, which can significantly affect the mechanical properties of sisal fibre-reinforced polymer composites.     

Al-Mn-Ce quasicrystalline composites: Phase formation and mechanical properties

Aluminium-based composites with quasicrystalline particles as reinforcements were synthesized via the powder metallurgy processing route. In order to obtain bulk samples with a nanoscale microstructure most equivalent to that resulting from rapid solidification, powders of Al-Mn-Ce alloys were prepared by pulverization of melt-spun ribbons using a planetary ball mill. Significant differences in the phase formation upon quenching, composite microstructure and thermal stability of the microstructure were found for different alloy compositions. Severe grain growth during the subsequent consolidation by hot extrusion caused the formation of a micrometre-scale composite instead of the nanoscale phase mixture initially existing after rapid solidification. After hot extrusion, the specimens were deformed by compression at a constant compression rate at room temperature. With an ultimate strength of up to 975 MPa and a ductility of more than 4% the material yields excellent properties compared with conventionally produced aluminium-based alloys.     

Morphology,conductivity, and mechanical properties of polypyrrole-containing composites

An electrical-conducting polypropylene/polypyrrole (PP/PPy) composite was prepared by the chemically oxidative modification reaction of pyrrole on the surface of PP particles in suspension. Another type of PP/PPy composite was prepared by mixing the coated PP particles with noncoated PP particles at room temperature. The composites were processed by compression molding or by injection molding. The injection-molded composites exhibited better mechanical properties compared to compression-molded samples, while these composites showed better antistatic behavior and electrical conductivity. The differences in the behavior of the two types of composites were caused by the different structure of the PPy phase, which was studied by hot-stage optical microscopy and X-ray photoelectron spectroscopy (XPS).     

Synthesis and mechanical properties of mechanically alloyed Al-Cu-Fe quasicrystalline composites

Al-Cu-Fe alloys were prepared by mechanical alloying starting from elemental powders in a high-energy planetary ball mill. Three different alloy compositions with the same c _Cu : c _Fe ratio of 2:1 but different aluminium contents, that is Al₅₅Cu₃₀Fe₁₅, Al₆₃Cu₂₅Fe₁₂ and Al₇₀Cu₂₀Fe₁₀, were investigated. A sequence of solid-state reactions resulting in quasicrystalline phase formation in Al₆₃Cu₂₅Fe₁₂ proceeds during milling and during annealing of the as-milled powder. These reactions were studied by X-ray diffraction, transmission electron microscopy and differential scanning calorimetry. In order to form an aluminium-matrix composite, Al₆₃Cu₂₅Fe₁₂ single-phase quasicrystalline powders were blended with different amounts of aluminium. In an intermediate milling step the powder blend was homogenized. The powders were consolidated by hot extrusion. The bulk samples revealed a homogeneous dispersion of the particles in the matrix but a rather heterogeneous size distribution. The mechanical properties at room temperature were tested by constant-rate compression tests. A rule-of-mixtures dependence of the ultimate strength and the yield strength on the volume fraction of the quasicrystalline particles was found.     

Electrostrictive conversion enhancement of polymer composites using a nonlinear approach

Recent trends in electromechanical conversion demonstrated the advantages of using electrostrictive polymers for actuation or energy harvesting. However, their conversion abilities are lower than usual electroactive materials, such as piezoelectrics. The purpose of this Letter is to propose a solution for artificially increasing the coupling factor of electrostrictive materials. Based on an intermittent switching on an electrical circuit that leads to a voltage increase as well as a reduced phase between voltage and velocity, it is shown that such a process allows increasing the converted energy by 1200% and a gain up to 4 in terms of transferred electrical energy.     

Morphology and mechanical properties of reconstituted wood board waste-polyethylene composites

The morphology and mechanical properties of reconstituted wood board waste-polyethylene composites were studied using virgin polyethylene (PE) and 2 wt% maleic anhydride (MA) modified polyethylene (MAPE) as matrices. Although the wood waste (WW) and PE are not compatible with each other, dynamic mechanical analyses (DMA) show considerable shifting in the α-transition temperature and crystallisation temperature (T _c) of PE in the unmodified composites, indicating physical interaction between PE and WW. The increase in crystallinity with increasing WW content up to 50 wt% indicates that WW is a potential nucleating agent for PE. However, the tensile strength of the unmodified composites gradually decreases with WW content, indicating that the improvement in interface adhesion is essential for WW to be used as reinforcing fillers. Fourier transform infrared spectroscopic (FTIR) results indicate that MAPE interacts with WW through esterification and hydrogen bonding to form good adhesion between the two phases. Inward shifting in glass transition temperature (T _g) for the MAPE-based composites containing less than 60 wt% WW indicates that WW and MAPE are partially compatible with each other. SEM micrographs of MAPE-based composites provide further evidence for this mechanism. The tensile strength of the MAPE-based composites is clearly higher than that of the virgin PE-based composites.     

Perspective: Kinetic and mechanical properties of adsorbed polymer layers

The European Physical Journal E -     

Dynamic conductivity of composites of fractal structure

We have studied the dynamic conductivity of a composite consisting of well- and weak-conducting components with random fractal structure. In order to calculate effective properties of composite medium, we used hierarchic structure model and innovative iterative averaging method based on renormalization group transformations idea. Our results show, that the behavior of a composite over a magnetic field become even more complicated.Unusual peaks and oscillations appear in frequency dependencies of effective conductivity, permittivity and other properties. We discuss the influence of fractal parameters of the composite structure on such unusual behavior of effective properties.