A straightforward wet-chemical route to the nanocomposites of general layered clays and metal sulfides

The nanocomposites of general layered clays and metal sulfides could be produced from reactions of the layered clay aqueous suspensions and water-soluble metal-thiourea complexes. The clay could be saponite, montmorillonite, hectorite and laponite, while the metal sulfide could be cobalt sulfide, nickel sulfide, zinc sulfide, cadmium sulfide, and lead sulfide. In the nanocomposites, the clay could be incorporated with the metal sulfide pillars and metal sulfide nanoparticles. (c) 2006 Elsevier B.V. All rights reserved.

Mg-based nanocomposites with high capacity and fast kinetics for hydrogen storage

Magnesium and its alloys have shown a great potential in effective hydrogen storage due to their advantages of high volumetric/ gravimetric hydrogen storage capacity and low cost. However, the use of these materials in fuel cells for automotive applications at the present time is limited by high hydrogenation temperature and sluggish sorption kinetics. This paper presents the recent results of design and development of magnesium-based nanocomposites demonstrating the catalytic effects of carbon nanotubes and transition metals on hydrogen adsorption in these materials. The results are promising for the application of magnesium materials for hydrogen storage, with significantly reduced absorption temperatures and enhanced ab/desorption kinetics. High level Density Functional Theory calculations support the analysis of the hydrogenation mechanisms by revealing the detailed atomic and molecular interactions that underpin the catalytic roles of incorporated carbon and titanium, providing clear guidance for further design and development of such materials with better hydrogen storage properties.

Effect of different preparation routes on the structure and properties of rigid polyurethane-layered silicate nanocomposites

To identify the effect of reactive preparation on the structure and properties of rigid polyurethane (PU)layered silicate nanocomposite, a range of nanocomposites were prepared by combining the various precursors in different sequences. The morphology of the samples was characterized by XRD and TEM. Tensile properties and dynamic mechanical thermal properties were measured. The reactions between the layered silicates and PU precursors were monitored via FTIR to gain an understanding of the participation of nanofiller in the polymerization reaction, and the impact of this on system stoichiometry. The XRD and TEM results provided evidence that morphology can differ significantly if different synthesis methods are used. However, the mechanical properties are dominated by the stoichiometry imbalance induced by the addition of the layered silicates. (c) 2006 Wiley Periodicals, Inc.

Effect of exfoliation and dispersion on the yield behavior of melt-compounded polyethylene-montmorillonite nanocomposites

The yield behavior of melt-mixed nanocomposites containing 5 wt % organically modified montmorillonite in matrices of a linear low-density polyethylene (LLDPE) or a modified polyethylene was studied as a function of the temperature. and strain rate. In the melt-mixed LLDPE nanocomposite, the montmorillonite showed a slight increase in the clay spacing, which suggested that the clay was at best intercalated. Transmission electron microscopy (TEM) images showed that the dispersion in this nanocomposite was poor. The use of the modified polyethylene promoted exfoliation of the clay tactoids in the nanocomposite, as assessed by X-ray diffraction and TEM. In both nanocomposites, the yield mechanisms were insensitive to the addition of the organoclay, even though modest increases in the modulus were produced. (c) 2006 Wiley Periodicals, Inc.

Phase behavior, crystallization, and nanostructures in thermoset blends of epoxy resin and amphiphilic star-shaped block copolymers

This article reports thermoset blends of bisphenol A-type epoxy resin (ER) and two amphiphilic four-arm star-shaped diblock copolymers based on hydrophilic poly(ethylene oxide) (PEO) and hydrophobic poly(propylene oxide) (PPO). 4,4'-Methylenedianiline (MDA) was used as a curing agent. The first star-shaped diblock copolymer with 70 wt% ethylene oxide (EO), denoted as (PPO-PEO)(4), consists of four PPO-PEO diblock arms with PPO blocks attached on an ethylenediamine core; the second one with 40 wt% EO, denoted as (PEO-PPO)(4), contains four PEO-PPO diblock arms with PEO blocks attached on an ethylenediamine core. The phase behavior, crystallization, and nanoscale structures were investigated by differential scanning calorimetry, transmission electron microscopy, and small-angle X-ray scattering. It was found that the MDA-cured ER/(PPO-PEO)(4) blends are not macroscopically phase-separated over the entire blend composition range. There exist, however, two microphases in the ER/(PPO-PEO)(4) blends. The PPO blocks form a separated microphase, whereas the ER and the PEO blocks, which are miscible, form another microphase. The ER/(PPO-PEO)(4) blends show composition-dependent nanostructures on the order of 10-30 nm. The 80/20 ER/(PPO-PEO)(4) blend displays spherical PPO micelles uniformly dispersed in a continuous ER-rich matrix. The 60/40 ER/(PPO-PEO)(4) blend displays a combined morphology of worm-like micelles and spherical micelles with characteristic of a bicontinuous microphase structure. Macroscopic phase separation took place in the MDA-cured ER/(PEO-PPO)(4) blends. The MDA-cured ER/(PEO-PPO)(4) blends with (PEO-PPO)(4) content up to 50 wt% exhibit phase-separated structures on the order of 0.5-1 mu m. This can be considered to be due to the different EO content and block sequence of the (PEO-PPO)(4) copolymer. (c) 2006 Wiley Periodicals, Inc.

Phase separation, porous structure, and cure kinetics in aliphatic epoxy resin containing hyperbranched polyester

Thermosetting blends of an aliphatic epoxy resin and a hydroxyl-functionalized hyperbranched polymer (HBP), aliphatic hyperbranched polyester Boltorn H40, were prepared using 4,4'-diaminodiphenylmethane (DDM) as the curing agent. The phase behavior and morphology of the DDM-cured epoxy/HBP blends with HBP content up to 40 wt% were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electron microscopy (SEM). The cured epoxy/HBP blends are immiscible and exhibit two separate glass transitions, as revealed by DMA. The SEM observation showed that there exist two phases in the cured blends, which is an epoxy-rich phase and an HBP-rich phase, which is responsible for the two separate glass transitions. The phase morphology was observed to be dependent on the blend composition. For the blends with HBP content up to 10 wt%, discrete HBP domains are dispersed in the continuous cured epoxy matrix, whereas the cured blend with 40 wt% HBP exhibits a combined morphology of connected globules and bicominuous phase structure. Porous epoxy thermosets with continuous open structures on the order of 100-300 nm were formed after the HBP-rich phase was extracted with solvent from the cured blend with 40 wt% HBP. The DSC study showed that the curing rate is not obviously affected in the epoxy/HBP blends with HBP content up to 40 wt %. The activation energy values obtained are not remarkably changed in the blends; the addition of HBP to epoxy resin thus does not change the mechanism of cure reaction of epoxy resin with DDM. (c) 2006 Wiley Periodicals, Inc.

Effects of carbon nanotubes and metal catalysts on hydrogen storage in magnesium nanocomposites

This paper reports a study on nanostructured magnesium composites with carbon nanotubes (CNTs) and catalytic transition metals with high H-2 adsorption capacity and fast adsorption kinetics at reduced hydrogenation temperatures. Nanostructures in such a composite are shown to be responsible for improvements in both adsorption capacity and kinetics. It is found that the carbon nanotubes significantly increase the hydrogen storage capacity, and the catalytic transition metals (Fe and Ti) greatly improve the kinetics. This could be understood from the enhancement of diffusion by CNTs and decrease in energy barrier of hydrogen dissociation at the magnesium surface.

Visoelastic studies on thermoplastic polyurethane nanocomposites using a nano-hardness tester

The viscoelastic behaviour of a range of polyurethane thermoplastic elastomer montmorillonite nanocomposites has been studied using a nanohardness tester. For softer Shore hardness 80A materials, the introduction of the organo-clay increased the creep strain obtained while the nano-indentor was held at constant load. The increase in creep strain was greatest for materials containing an organo-clay modified with a more hydrophilic quaternary alkylammonium surfactant and with higher loadings of the hydrophilic organo-clay. This suggested the effect might be due to a plasticising effect of the excess surfactant. For the harder Shore hardness 55D materials, the addition of the organo-clays produced only a small decrease in the creep strain, probably due to the interconnected hard domains in this material.

Effect of the average soft-segment length on the morphology and properties of segmented polyurethane nanocomposites

Two organically modified layered silicates (with small and large diameters) were incorporated into three segmented polyurethanes with various degrees of microphase separation. Microphase separation increased with the molecular weight of the poly(hexamethylene oxide) soft segment. The molecular weight of the soft segment did not influence the amount of polyurethane intercalating the interlayer spacing. Small-angle neutron scattering and differential scanning calorimetry data indicated that the layered silicates did not affect the microphase morphology of any host polymer, regardless of the particle diameter. The stiffness enhancement on filler addition increased as the microphase separation of the polyurethane decreased, presumably because a greater number of urethane linkages were available to interact with the filler. For comparison, the small nanofiller was introduced into a polyurethane with a poly(tetramethylene oxide) soft segment, and a significant increase in the tensile strength and a sharper upturn in the stress-strain curve resulted. No such improvement occurred in the host polymers with poly(hexamethylene oxide) soft segments. It is proposed that the nanocomposite containing the more hydrophilic and mobile poly(tetramethylene oxide) soft segment is capable of greater secondary bonding between the polyurethane chains and the organosilicate surface, resulting in improved stress transfer to the filler and reduced molecular slippage. (c) 2006 Wiley Periodicals, Inc.

Effect of fluoromica platelet size on the properties of segmented polyurethane nanocomposites

Segmented polyurethane nanocomposites containing three different size fractions of SomasifTM ME100 (synthetic fluoromica) have been prepared via solvent casting. The platelet size was adjusted via a proprietary milling process, and average diameters of approximately 500 nm, 100 nm and 30 nm were measured via TEM. To the best of our knowledge this is the first time the effect of aspect ratio has been studied with the same t-o-t structured mineral. The mechanical properties of these nanocomposites have been found to be highly dependent upon the platelet size. Depending on the aspect ratio and surface treatment selected, significant improvements in tensile strength can be achieved with a minimal reduction in resilience: a problem encountered with elastomeric layered silicate nanocomposites.