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We report a large reduction in contact resistance between stretchable carbon nanotube/silicone rubber composites and silver electrodes by a chemical surface treatment, accompanied by an enhancement in the electrical conductivity of the composites. The reactive solvent, trifluoroacetic acid, works for the purpose. In addition, the treatment makes a uniform etching in a micro level with little sacrifice in surface roughness of the nanocomposites. The electrical conductivity of 1.0 wt% nanotube composite was enhanced approximately two-fold and three-fold by ten- and thirty-second treatment, which was induced by the reduction in the contact resistance to one half of an original value. It is meaningful that our finding can be an approach to reduce the nanoparticle loading while keeping electrical conductivity in a high level, which can be crucial for securing flexibility or stretchability in a viewpoint that the elongation is inversely proportional to the conductive particle loading. [ABSTRACT FROM AUTHOR]

In the recent decades, the phenomena of space charge accumulation in the high voltage direct current (HVDC) insulation have attracted more and more attention. In this paper, the gradient-distribution multi-layered Al 2 O 3 /low density polyethylene (LDPE) nanocomposites were prepared via layer-by-layer melting blending and hot pressing method. Morphologies and electrical properties of these gradient-distribution structured composites were discussed. Results showed that this unique structure could largely enhance the breakdown strength of LDPE. The breakdown strength of the LDPE nanocomposites varied with nano-Al 2 O 3 concentrations, and it could reach to 200 kV/mm for the LDPE nanocomposites. Besides, space charge of the LDPE nanocomposites was measured by pulsed electro-acoustic (PEA) method. The charge profiles indicated that space charge suppression of the gradient-distribution multi-layered composites was better than that of the monolayer ones with general mean-distribution structure. Their excellent insulating properties were attributed to the trap which exists in the surface, and that could well inhibit the charge injecting into the materials. [ABSTRACT FROM AUTHOR]

The study of interfacial interactions between polymer matrix and particulate fillers is essential for producing composites with enhanced properties. In this work, the influence of the unique glassy carbon (GC) structure on the properties of its binary epoxy composites as well as hybrid nanocomposites with GC and multi-walled carbon nanotubes (MWCNTs) was investigated. The purpose of incorporating MWCNTs into the epoxy matrix (EP) as an addition filler was to obtain nanocomposites with improved properties. The influence of GC particles alone or in combination with MWCNTs on morphological, thermomechanical, and electrical properties of composites was studied in detail. There were found good, homogeneous dispersion of GC and MWCNTs in epoxy matrix as well as strong interfacial interactions between the carbon fillers and epoxy. Mechanical measurements demonstrated that both the tensile and bending properties of the composites, especially the hybrid composites, were greatly improved compared with those of pure epoxy due to the uniform dispersion of fillers in epoxy and significant adhesion between the filler and matrix. The electrical resistivity of hybrid composites, which is directly related to the presence of MWCNTs in addition to the GC, decreased sharply by 9–11 orders of magnitude compared to the insulating matrix. Such composites with enhanced mechanical and electrical properties could be applied in various branches of industry. [ABSTRACT FROM AUTHOR]

Magnetic and electrically conductive epoxy nanocomposites are fabricated by compounding thermally reduced graphene oxide (TGO) and magnetic carbonyl iron (CI) using a solvent-free and efficient centrifugal mixing method. The addition of TGO sheets not only forms an interconnected conducting network within the epoxy matrix, but also prevents the aggregation of heavy CI components. The incorporation of CI components leads to obvious increases in permeability, magnetic loss, and electromagnetic interference (EMI) shielding properties. Among different shapes of CI components, spherical CI particles result in the best EMI shielding performance. The ternary nanocomposites exhibit excellent shielding effectiveness (>36 dB within 9.5–12 GHz) and a maximum value of ∼40 dB at 11.7 GHz, much higher than that (∼20 dB) of epoxy/TGO nanocomposite with the same content of TGO. Wave absorption loss is confirmed to be the main EMI shielding mechanism for the epoxy nanocomposites. The high EMI shielding performance makes the epoxy nanocomposites promising for EMI shielding applications. [ABSTRACT FROM AUTHOR]

Pyrene moieties containing amide functional groups with various alkyl chain lengths (butyl, octyl, and dodecyl) were synthesized and utilized in non-covalent functionalization of the surface of multi-walled carbon nanotubes (MWNTs). The D/G ratio of the MWNTs (derived from the Raman spectra) remained unchanged upon non-covalent functionalization of the surface of MWNTs, indicating that there were no increases in the number of defect sites on the surface of the MWNTs. PA 6 (polyamide 6)/MWNT nanocomposites were prepared by the melt-compounding method for evaluation of the mechanical and electrical properties. Flexural testing confirmed the much higher flexural modulus of the PA 6/non-covalently functionalized MWNTs relative to the PA 6/pristine MWNT nanocomposites. Furthermore, the PA 6/non-covalently functionalized MWNT nanocomposites exhibited better electrical properties due to preservation of the intrinsic structure of the MWNTs as well as the uniform dispersion of the MWNTs in the PA 6 matrix, which also played a role in the enhanced mechanical properties. It could be observed that the longer alkyl chain length of the pyrene moieties led to further improvement of the sheet resistance and mechanical properties, which is attributed to the enhanced compatibility with PA 6 derived from functionalization. [ABSTRACT FROM AUTHOR]

Abstract: The use of nanoparticles in polymer composite dielectrics has promised great improvements, but useful results have been elusive. Here, the importance of the interfacial interactions between the nanoparticles and the polymer matrix are investigated in TiO2 nanocomposites for dielectric materials using surface functionalisation. The interface is observed to dominate the nanocomposite properties and leads to a threefold increase in permittivity at volume fractions as low as 10%. Surface functionalisation of the filler nanoparticles with silanes allows control of this interface, avoiding significant degradation of the other important material properties, particularly electrical breakdown strength, and resulting in a material that is demonstrated successfully as an active material in a dielectric elastomer actuator application with increased work output compared to the pure polymer. Although further permittivity increases are observed when the interface regions have formed a percolation network, the other material properties deteriorate. The observation of percolation behaviour allows the interface thickness to be estimated. [Copyright &y& Elsevier]

Abstract: A study of the requirements necessary to fabricate novel MWCNT buckypaper/benzoxazine nanocomposites, based on rheological results, is presented. Best conditions to infiltrate the resin, without any diluents, in the buckypaper are selected from viscosity data obtained under time–temperature cycles. Infiltration results are analyzed using SEM microphotographs. The nanocomposite is obtained after an adequate curing process of the benzoxazine impregnated buckypaper. The mechanical and electrical properties of the nanocomposite are investigated. The obtained electrical conductivity values are several orders of magnitude larger than the values reported for conventional CNT/polymer nanocomposites. [Copyright &y& Elsevier]

Abstract: Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41vol.% and high electrical conductivity of ∼0.028S/m with only ∼1.64vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites. [Copyright &y& Elsevier]

Abstract: A comparative study of the influence of processing route on polyurethanes (PUs)/multiwalled carbon nanotube (MWCNT) composites mechanical and electrical properties and also morphology was undergone employing two differentiated processing methods, solvent casting and buckypaper infiltration, for producing PU composites with low, medium and high mass fractions of acid treated MWCNT, and with no covalent linkages between the matrix and the nanotubes. As for example, with a MWCNT mass fraction of ∼18wt.% the second method produced stiffer (270MPa), lighter (948kgm−3) and more electrically conductive (1.8Scm−1) composite while the first one gave softer (111MPa) and more ductile (141%) materials. These properties differences are related to the different PU/MWCNT dispositions obtained through each synthesis route. Nanotubes percolating concentration is found to be crucial on composite properties evolution and a preferential interaction of MWCNT with PU hard segments is observed for solvent cast composites. [Copyright &y& Elsevier]

Abstract: Four dispersion methods were used for the preparation of vapour grown carbon nanofibre (VGCNF)/epoxy composites. It is shown that each method induces certain levels of VGCNF dispersion and distribution within the matrix, and that these have a strong influence on the composite electrical properties. A homogenous VGCNF dispersion does not necessarily imply higher electrical conductivity. In fact, it is concluded that the presence of well distributed clusters, rather than a fine dispersion, is more important for achieving larger conductivities for a given VGCNF concentration. It is also found that the conductivity can be described by a weak disorder regime. [Copyright &y& Elsevier]