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In general, dielectric multifiller polymer composites have the potential to achieve enhanced performances by integrating the desirable properties of each filler. However, the improvement in thermophysical and dielectric properties is often accompanied by a deterioration of electrical breakdown strength (EBD). Here, we explore a two-filler polymer nanocomposite structure, based on polyolefins with montmorillonite and calcium carbonate fillers, and present an effective approach to obtain enhanced EBD by tailoring the composite morphology (by designing the pseudo-two-dimensional nanoclays to preferentially physisorb on the surfaces of calcium carbonates, so as to change the nature of the filler/polymer interfaces). It is shown that, in these structured polymer nanocomposites, the breakdown performance is substantially improved, exceeding the performance of the unfilled polymers and of the respective single-filler composites. The enhanced dielectric behavior originates from the specific composite morphology, ...

Emerging energy and insulation applications require dielectric materials that can operate at high electric fields and meanwhile possess low leakage currents. For dielectric polymer nanocomposites, beyond filler dispersion, tailoring hierarchical structures offers a promising, yet largely untapped, approach to reach this goal. Here, we demonstrate that the controlled arrangement of pseudo-2D nanofillers and polymer crystals in polyethylene/montmorillonite nanocomposites can be used as an effective approach to achieve nontrivial highly enhanced dielectric performances, far beyond what is feasible with conventional (macroscopic, isotropic) composites. In particular, it is shown that aligned nanofillers can increase the breakdown strength, while, at the same time, reducing the leakage current, in these dielectric nanostructured composites. The orientation of the nanosized pseudo-2D fillers increases the path tortuosity for charge transport, acting as an effective geometric barrier, in the same way and in addi...

Glassy and rubbery epoxy–clay nanocomposites were synthesized by using various montmorillonite organoclays in order to investigate and compare the effect of the type of alkylammonium ion clay modifier on the structure and properties of the nanocomposites. The organoclays studied were the Nanomer I.28E and I.30E and the Cloisite C10A, C15A and C20A. The functionality (acidity), size and shape of backbone chain, hydrophobicity and polarity were the varying parameters of the organic modifiers that were correlated to the ability of the organoclays to form highly intercalated or exfoliated nanocomposites and to the changes observed in the mechanical (tensile measurements), thermo-mechanical (DMA) and thermal (TGA) properties of the epoxy nanocomposites. The primary alkylammonium ion modifiers with reactive/acidic hydrogen atoms, compared to the quaternary octadecyl, dihydrogenated tallow and benzyl-substituted hydrogenated tallow ammonium ions, were the most effective for the formation of exfoliated clay glassy and rubbery epoxy nanocomposites which exhibited improved properties compared to the pristine epoxy polymers.

Low-density polyethylene (LDPE)/silicate nanocomposites were prepared by the melt compounding and solution blend methods using unmodified LDPE polymer and layered silicates with different aspect ratio. X-ray diffraction (XRD) analysis performed on composites obtained by dispersing the organosilicates in molten LDPE evidenced an exfoliated or partially exfoliated structure for the low aspect ratio silicate (laponite) in contrast to the high aspect ratio silicate (montmorillonite), which led to the formation of intercalated nanocomposites. With regard to the preparation method, the melt compounding method was more effective in forming exfoliated/highly intercalated LDPE nanocomposites compared with the solution blend method (using CCl4 as a solvent). A gradual increase in crystallization temperatures (Tc) with increasing laponite content for LDPE-organolaponite nanocomposites was revealed by differential scanning calorimetry (DSC) measurements. Thermogravimetric analysis and tensile measurements results indicated that thermal stability and elastic modulus increment were more prevalent for nanocomposites prepared using organomontmorillonite as filler. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

The use of homoionic organic clays and mixed-ion organic/inorganic clays modified by di- or triamines (Jeffamines), which are being used as epoxy resin curing agents, in the synthesis of polymer nanocomposites has been studied in this work. Our aim is to enhance polymer crosslinking and interfacial adhesion in the nanocomposite structure by utilizing the functionality of the di/triamines on the surface of clay nanolayers and by reducing the organic modifier via formation of homostructured mixed-ion organic/inorganic clays. The results show that the use of homoionic organic clays exchanged with relatively short chain di- or triamines and mixed-ion organic/inorganic clays partially exchanged (ca. 35%) with long chain diamines resulted in intercalated structures with enhanced thermo-mechanical properties (Young's Modulus, Storage Modulus). On the other hand, homoionic organic clays exchanged with long chain diamines and triamines resulted in exfoliated nanocomposites but with compromised mechanical properties due to the plasticizing effect of the long chain amine modifiers.

MgO supported bimetallic catalysts containing a combination of Fe and Ni metals in 1:1 ratio at varying loadings (from 1 to 50 wt.%) were prepared by a wet impregnation method. Carbon nanotubes were synthesized over the prepared catalysts by the catalytic decomposition of acetylene for different reaction conditions. The effect of reaction temperature, reaction time and metal loading to the yield, structural perfection and morphology of the synthesized carbon products was investigated using a combination of XRD, DTA/DTG, Raman spectroscopy and Scanning Electron Microscopy (SEM) techniques. The results revealed that both the selection of the growing conditions and the metal loading are critical for the nature of the synthesized carbon nanotubes and can assign their yield and their overall quality. The synthesized carbon nanotubes exhibit extended crystallinity while they were synthesized at high yields.

Extrusion blown polyethylene and polyethylene/montmorillonite nanocomposite films were cold stretched to various ratios to quantify the influence of the crystal orientation and the nanofiller alignment on their dielectric breakdown performance. It was found that the crystal orientation could increase the breakdown strength (EBD) in the stretched blown films. The aligned pseudo-2D inorganic nanoclays provided additional strong improvements in EBD that can be superimposed to any EBD enhancement due to the polymer crystal orientation. At high filler loadings and high stretching ratios, the onset of percolation was observed through a substantial improvement in the dielectric breakdown strength.

The purpose of the present work was to study the corrosion behavior of steel coated with epoxy-(organo) clay nanocomposite films. The investigation was carried out using salt spray exposures, optical and scanning electron microscopy examination, open circuit potential, and electrochemical impedance measurements. The mechanical, thermomechanical, and barrier properties of pristine glassy epoxy polymer and epoxy-clay nanocomposites were examined. The degree of intercalation/exfoliation of clay nanoplatelets within the epoxy polymer also was determined. The mechanical, thermomechanical, and barrier properties of all the epoxy-clay nanocomposites were improved compared to those of the pristine epoxy polymer. In addition, both the pristine epoxy and the epoxy nanocomposite coatings protected the steel from corrosion. Furthermore, the protective properties of the nanocomposite coatings were superior compared to those of the pristine epoxy polymer. The protective properties of the nanocomposite coatings varied with the modified clay used. The epoxy-montmorillonite clay modified with primary octadecylammonium ions, Nanomer I.30E, had a better behavior than that modified with quaternary octadecylammonium ions, Nanomer I.28E.