Showing papers on "Nanocomposite published in 1998"

Nanocomposite polymer electrolytes for lithium batteries

Abstract: Ionically conducting polymer membranes (polymer electrolytes) might enhance lithium-battery technology by replacing the liquid electrolyte currently in use and thereby enabling the fabrication of flexible, compact, laminated solid-state structures free from leaks and available in varied geometries1. Polymer electrolytes explored for these purposes are commonly complexes of a lithium salt (LiX) with a high-molecular-weight polymer such as polyethylene oxide (PEO). But PEO tends to crystallize below 60 °C, whereas fast ion transport is a characteristic of the amorphous phase. So the conductivity of PEO–LiX electrolytes reaches practically useful values (of about 10−4 S cm−1) only at temperatures of 60–80 °C. The most common approach for lowering the operational temperature has been to add liquid plasticizers, but this promotes deterioration of the electrolyte's mechanical properties and increases its reactivity towards the lithium metal anode. Here we show that nanometre-sized ceramic powders can perform as solid plasticizers for PEO, kinetically inhibiting crystallization on annealing from the amorphous state above 60 °C. We demonstrate conductivities of around 10−4 S cm−1 at 50 °C and 10−5 S cm−1 at 30 °C in a PEO–LiClO4 mixture containing powders of TiO2 and Al2O3 with particle sizes of 5.8–13 nm. Further optimization might lead to practical solid-state polymer electrolytes for lithium batteries.

Nanolayer Reinforcement of Elastomeric Polyurethane

Abstract: The first examples of thermoset polyurethane−clay nanocomposites have been prepared by curing a polyurethane network in the presence of alkylammonium-exchanged forms of montmorillonite. A unique stress−strain behavior was observed for the elastomeric nanocomposites. The reinforcement effects of the silicate nanolayers not only greatly improved the tensile properties of the matrix but the strain-at-break also increased with increasing clay loading. Thus, nanocomposite formation both strengthens and toughens the elastomeric matrix compared to the pristine polymer.

Polymer-layered silicate nanocomposites: Synthesis, properties and applications

Abstract: Polymer nanocomposites, especially polymer-layered silicate (PLS) nanocomposites, represent a radical alternative to conventionally (macroscopically) filled polymers. Because of their nanometer-size dispersion, the nanocomposites exhibit markedly improved properties when compared with the pure polymers or conventional composites. These include increased modulus and strength, decreased gas permeability, increased solvent and heat resistance and decreased flammability. In addition to their potential applications, PLS nanocomposites are also unique model systems to study the structure and dynamics of polymers in confined environments. Using both delaminated and intercalated hybrids, the statics and dynamics of polymers confined over distances ranging from the radius of gyration of the polymer to the statistical segment length of the chains can be studied. © 1998 John Wiley & Sons, Ltd.

Continuous self-assembly of organic–inorganic nanocomposite coatings that mimic nacre

Abstract: Nanocomposite materials are widespread in biological systems Perhaps the most studied is the nacre of abalone shell, an orientated coating composed of alternating layers of aragonite (CaCO3) and a biopolymer Its laminated structure simultaneously provides strength, hardness and toughness: containing about 1 vol % polymer, nacre is twice as hard and 1,000 times as tough as its constituent phases1 Such remarkable properties have inspired chemists and materials scientists to develop synthetic, ‘biomimetic’ nanocomposite assemblies2,3,4,5 Nonetheless, the efficient processing of layered organic–inorganic composites remains an elusive goal Here we report a rapid, efficient self-assembly process for preparing nanolaminated coatings that mimic the structure of nacre Beginning with a solution of silica, surfactant and organic monomers, we rely on evaporation during dip-coating to induce the formation of micelles and partitioning of the organic constituents into the micellar interiors6 Subsequent self-assembly of the silica–surfactant–monomer micellar species into lyotropic mesophases7 simultaneously organizes the organic and inorganic precursors into the desired nanolaminated form Polymerization fixes this structure, completing the nanocomposite assembly process This approach may be generalized both to other composite architectures and to other materials combinations

Processing and properties of carbon nanotubes-nano-SiC ceramic

Abstract: Carbon nanotubes–nano-SiC ceramic has been fabricated by the hot-press method. The preparation steps involved the use of dispersing nano-SiC powders and carbon nanotubes in butylalcohol using an ultrasonic shaker. The reasonable relative density of about 95% has been achieved by hot-pressing at 2273 K (at 25 MPa in Ar for 1 h). The three-point bending strength and fracture toughness of the composite has about 10% increment over monolithic SiC ceramic which was fabricated under the same process. The reasons for the increment are the strengthening and toughening role of carbon nanotubes occuring in the matrix.

High energy products in rapidly annealed nanoscale Fe/Pt multilayers

Abstract: Magnetic properties of nanocomposite Fe–Pt films with Fe concentration higher than 50 at % have been investigated in this study. Fe/Pt multilayers were produced by sputtering and magnetic hardening was observed after heat treatment including rapid annealing. The final nanocomposite films consisted of the hard face-centered tetragonal FePt phase and a soft face-centered-cubic phase. The maximum energy products of the optimally processed samples exceeded 40 MGOe. Evidence for exchange coupling of the hard and soft phases was found.

Nanocomposites based on montmorillonite and unsaturated polyester

Abstract: The concept of nanoscale reinforcement provides opportunity for synthesis of new polymer materials with unique properties. Montmorilonite (MMT) was derived from bentonite, purified, activated by sodium ions and mixed with reacting unsaturated polyester (UP). X-ray and transmission electron microscopy data were in support of the formation of a partially delaminated nanocomposite material. At an MMT content of only 1.5 vol%, the fracture energy, G Q , of the nanocomposite was doubled, 138 J/m 2 as compared with 70 J/m 2 for the pure UP.

A new conception on the toughness of nylon 6/silica nanocomposite prepared via in situ polymerization

Abstract: A novel method, in situ polymerization, was used for the preparation of nylon 6/silica nanocomposites, and the mechanical properties of the nanocomposites were examined. The results showed that the tensile strength, elongation at break, and impact strength of silica-modified nanocomposites exhibited a tendency of up and down with the silica content increasing, while those of silica-unmodified nanocomposites decreased gradually. It also exhibited that the mechanical properties of silica-modified nanocomposites have maximum values only when 5% silica particles were filled. Based on the relationship between impact strength of the nanocomposites and the matrix ligament thickness τ, a new criterion was proposed to explain the unique mechanical properties of nylon 6/silica nanocomposites. The nylon 6/silica nanocomposites can be toughened only when the matrix ligament thickness is less than τc and greater than τa, where τa is the matrix ligament thickness when silica particles begin to aggregate, and τc is the critical matrix ligament thickness when silica particles begin to toughen the nylon 6 matrix. The matrix ligament thickness, τ, is not independent, which related with the volume fraction of the inorganic component because the diameter of inorganic particles remains constant during processing. According to the observation of Electron Scanning Microscope (SEM), the process of dispersion to aggregation of silica particles in the nylon 6 matrix with increasing of the silica content was observed, and this result strongly supported our proposal. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 789–795, 1998

Nanostructured fillers and carriers

Abstract: A nanocomposite structure comprising a nanostructured filler or carrier intimately mixed with a matrix, and methods of making such a structure. The nanostructured filler has a domain size sufficiently small to alter an electrical, magnetic, optical, electrochemical, chemical, thermal, biomedical, or tribological property of either filler or composite by at least 20%.

Polyamide 6/silica nanocomposites prepared by in situ polymerization

Abstract: A polyamide 6 (PA 6)/silica nanocomposite was obtained through a novel method, in situ polymerization, by first suspending silica particles in ϵ-caproamide under stirring and then polymerizing this mixture at high temperature under a nitrogen atmosphere The silicas were premodified with aminobutyric acid prior to the polymerization The effects of the addition of unmodified and modified silicas on the dispersion, interfacial adhesion, isothermal crystallization, and mechanical properties of PA 6 nanocomposites were investigated by using scanning electron microscopy, dynamic mechanical analysis, differential scanning calorimetry, and mechanical tests, respectively The results show that the silicas dispersed homogeneously in the PA 6 matrix The addition of silicas increases the glass transition temperature and crystallization rate of PA 6 The mechanical properties such as impact strength, tensile strength, and elongation at break of the PA 6/modified silica nanocomposites showed a tendency to increase and decrease with increase of the silica content and have maximum values at 5% silica content, whereas those of the PA 6/unmodified silica system decreased gradually © 1998 John Wiley & Sons, Inc J Appl Polym Sci 69: 355–361, 1998

Load-adaptive crystalline–amorphous nanocomposites

Abstract: Advances in laser-assisted deposition have enabled the production of hard composites consisting of nanocrystalline and amorphous materials Deposition conditions were selected to produce super-tough coatings, where controlled formation of dislocations, nanocracks and microcracks was permitted as stresses exceeded the elastic limit This produced a self-adjustment in the composite deformation from hard elastic to quasiplastic, depending on the applied stress, which provided coating compliance and eliminated catastrophic failure typical of hard and brittle materials The load-adaptive concept was used to design super-tough coatings consisting of nanocrystalline (10–50 nm) TiC grains embedded in an amorphous carbon matrix (about 30 vol%) They were deposited at near room temperature on steel surfaces and studied using X-ray photoelectron spectroscopy, X-ray diffraction, scanning electron microscopy, Raman spectroscopy, nanoindentation and scratch tests Design concepts were verified using composition–structure–property investigations in the TiC–amorphous carbon (a-C) system A fourfold increase in the toughness of hard (32 GPa) TiC–a-C composites was achieved in comparison with nanocrystalline single-phase TiC

In Situ Synthesis of Polymer−Clay Nanocomposites from Silicate Gels

Abstract: Polymer-containing silicate gels were hydrothermally crystallized to form layered magnesium silicate hectorite clays containing polymers that are incorporated in situ. Gels consist of silica sol, magnesium hydroxide sol, lithium fluoride, and the polymer of choice. Dilute solutions of gel in water are refluxed for various lengths of time and then isolated via centrifugation, washed, and air-dried. Polymer loadings up to 86% were attained by adding more polymer to the solutions after 2-day reaction times, reacting for another 24 h, and continuing this process prior to isolation. Polyaniline (PANI)- and polyacrylonitrile (PACN)-clay samples contain up to 57% and 76% polymer, respectively, after just one sequential addition at high polymer loading. Series of PANI-, PACN-, poly(vinylpyrrolidone) (PVP)-, and hydroxypropylmethylcellulose (HPMC)-clays also were prepared by several sequential additions of lower polymer loading to the silicate gel during crystallization. Final polymer loadings were determined by thermal analysis. Basal spacings between clay interlayers were measured by X-ray powder diffraction for all samples. Increases in polymer loadings and basal spacings were observed for all the neutral polymers studied, until or unless delamination occurred. Delamination was evident for PACN- and PANI-clay nanocomposites. The highest loadings were observed for the PACN-clays, up to 86%. For the cationic polymermore » polydimethyldiallylammonium chloride, however, the loading could not be increased beyond about 20%. This is due to electrostatic interactions that balance the negatively charged sites on the silicate lattice with those on the cationic polymer chain. Beyond charge compensation, there is no driving force for further incorporation. Charge compensation in the case of the neutral polymers is attained by interlayer lithium(I) cations.« less

Carbon nanotubes–Fe–Alumina nanocomposites. Part II: microstructure and mechanical properties of the hot-Pressed composites

Abstract: Carbon nanotubes-Fe-Al2O3 massive composites have been prepared by hot-pressing the corresponding composite powders, in which the carbon nanotubes are arranged in bundles smaller than 100 nm in diameter and several tens of micrometers long, forming a web-like network around the Fe-Al2O3 grains. In the powders, the quantity and the quality of the carbon nanotubes both depend on the Fe content (2, 5, 10, 15 and 20 wt%) and on the reduction temperature (900 or 1000°C) used for the preparation. Bundles of carbon nanotubes are present in the hot-pressed materials but with a decrease in quantity in comparison to the powders. This phenomenon appear to be less pronounced for the powders containing higher-quality carbon, i. e. a higher proportion of nanotubes with respect to the total carbon content. The presence of carbon as nanotubes and others species (Fe carbides, thick and short tubes, graphene layers) in the powders modifies the microstructure of the hot-pressed specimens in comparison to that of similar carbon-free nanocomposites : the densifications are lower, the matrix grains and the intergranular metal particles are smaller. The fracture strength of most carbon nanotubes-Fe-Al2O3 composites is only marginally higher than that of Al2O3 and are generally markedly lower than those of the carbon-free Fe-Al2O3 composites. The fracture toughness values are lower than or similar to that of Al2O3. However, SEM observations of composite fractures indicate that the nanotubes bundles, which are very flexible, could dissipate some fracture energy.

Ultrathin Molybdenum Polyoxometalate−Polyelectrolyte Multilayer Films

Abstract: Ultrathin multilayer films of a novel molybdenum(VI) polyoxometalate cluster ((NH4)21[H3Mo57V6(NO)6O183(H2O)18]) (Mo57) and poly(allylamine hydrochloride) (PAH) have been prepared by the consecutive stepwise adsorption of Mo57 and PAH from dilute aqueous solution. The Mo57/PAH multilayer films have been characterized by optical spectroscopy and small-angle X-ray reflectivity (XR) methods. UV−vis measurements reveal regular film growth with each Mo57 adsorption. The average Mo57 surface density was found to be (1.4 ± 0.4) × 1013 clusters per cm2, corresponding to an average surface coverage of 56 ± 12%. XR experiments confirm uniform film growth, with the film thickness increasing with each Mo57 adsorption step. The average thickness for the Mo57/PAH layer pair was determined to be 0.8 ± 0.1 nm. The Mo57 density in the film can be readily controlled by varying the polyelectrolyte interlayer separation between each Mo57 layer, and the total film thickness can be controlled by altering the number of adsorpti...

Characterization of epoxy–clay hybrid composite prepared by emulsion polymerization

Abstract: This article demonstrates the direct intercalation of an epoxy polymer in the interlayer of Na+–montmorillonite (MMT) by a step type of polymerization in an aqueous emulsion media. The synthesis and the results of structural and thermal characterizations for this hybrid composite are described. Equimolar quantities of bisphenol A and an epoxy prepolymer (n = 0.2) in an emulsion media were polymerized in the presence of Na+–MMT. X-ray diffraction (XRD) data obtained from the acetone-extracted products show that the basal spacing of the MMT is expanded from 0.96 to 1.64 nm. Thermal characterization for the postcured products by TGA and DSC gave evidence of enhanced thermal stabilities. SEM examination of the uncured products revealed that a disordered phase begins to appear with increasing polymer loading. However, the XRD profile supported that an overwhelming fraction of the nanocomposite contains intercalated clay. Also, the possibility of intercalation by the emulsion technique is proposed on the basis of the swelling characteristics of MMT in aqueous media and the sizes of micelles containing a monomer. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 68: 1997–2005, 1998

Mechanically alloyed nanocomposite magnets (invited)

Abstract: Nanocomposites, consisting of a hard magnetic rare earth–transition metal phase exchange coupled to soft magnetic α-Fe or α-(Fe,Co), exhibit enhancement of the remanent magnetization due to exchange coupling across interfaces between grains. Modeling studies have shown that crystallite sizes of less than 20 nm are generally required for significant remanence enhancement and values of remanent magnetization equal to 70%–80% of saturation magnetization have been reported in mechanically alloyed two phase mixtures of α-Fe and a hard magnetic phase, such as Nd2Fe14B. Studies of microstructural evolution during mechanical alloying have shown that as-milled structures consist of a magnetically soft two phase mixture of α-Fe and an amorphous phase. Similar microstructures are observed regardless of whether mechanical milling or mechanical alloying has been carried out. Heat treatment above a critical temperature is required to crystallize grains of the hard magnetic phase. The formation of metastable intermediat...

Mechanical properties of Ti-containing and W-containing diamond-like carbon coatings

Abstract: Ti-containing and W-containing diamond-like hydrocarbon coatings have been synthesized by glow discharge reactive magnetron sputter deposition in an Ar/CH4 mixture. it is shown that these metal-containing hydrocarbon coatings consist of nanocrystalline TiC and WC embedded in an amorphous hydrocarbon matrix and are thin-film nanocomposite materials. The elastic modulus and hardness of these nanocomposites exhibit systematic dependence on their composition, while the ratio of hardness to modulus remains approximately a constant. It is also shown that the elastic modulus and hardness of these nanocomposites are within macromechanical bounds for two-phase composite materials.

Fabrication and mechanical properties of 5 vol% copper dispersed alumina nanocomposite

Abstract: An optimum route to fabricate the Al 2 O 3 Cu nano-composite with sound microstructure and desired mechanical properties was investigated. Two methods for developing a uniform dispersion of Cu particles in Al 2 O 3 were compared on the basis of the resulting microstructures and mechanical properties. SEM and TEM analyses for the composites fabricated by reduction and sintering process using Al 2 O 3 CuO powder mixture showed that the nano-sized Cu particles were well distributed and situated on the grain boundaries of the Al 2 O 3 matrix. The composite, hot-pressed at 1450 °C, exhibited the maximum fracture strength and enhanced toughness compared with monolithic Al 2 O 3 . The strengthening was mainly attributed to the refinement of Al 2 O 3 matrix grains. The toughening mechanism in Al 2 O 3 Cu composite was discussed by the observed microstructural features and theoretical predictions based on crack bridging model and thermal residual stress effect.

CoPt/Ag nanocomposites for high density recording media

Abstract: Nanocomposite CoPt/Ag films have been successfully fabricated and their microstructural and magnetic properties have been investigated for potential applications in magnetic recording media. This was done by first making sputtered CoPt/Ag multilayers with the face-centered cubic (fcc) structure which is magnetically soft and then annealing the multilayers to transform the fcc phase to the highly anisotropic face-centered tetragonal phase (fct) which is magnetically hard. The final nanocomposite structure consists of CoPt nanoparticles with the hard fct phase embedded in a fcc Ag matrix. Large values of coercivity in the range of 1–17 kOe were achieved with grain sizes in the range of 7–100 nm, respectively.

Formation of crystalline nanoclusters of Fe2P, RuP, Co2P, Rh2P, Ni2P, Pd5P2, or PtP2 in a silica xerogel matrix from single-source molecular precursors

Abstract: Metal complexes containing bifunctional phosphine ligands that possess alkoxysilyl functional groups have been prepared for seven metals of the first, second, or third transition metal series. Incorporation of these single-source precursors into silica xerogel matrixes using sol−gel chemistry affords molecularly doped xerogels. Subsequent thermal treatment of these doped xerogels under solely reducing conditions selectively affords nanoclusters of Fe2P, RuP, Co2P, Rh2P, Ni2P, Pd5P2, or PtP2 which are highly dispersed throughout the bulk of the xerogel matrix. Characterization of these nanocomposite materials by transmission electron microscopy, energy-dispersive spectrometry, X-ray diffraction, and electron diffraction indicates that the metal phosphide nanoclusters are highly crystalline with some exhibiting nonspherical morphology.

Carbon nanotubes–Fe–alumina nanocomposites. Part I: influence of the Fe content on the synthesis of powders

Abstract: Oxides based on a-alumina and containing various amounts of Fe (2, 5, 10, 15 and 20 cat.%) were prepared by decomposition and calcination of the corresponding mixed-oxalates. Selective reduction of the oxides in a H2-CH4 atmosphere produces nanometric Fe particles which are active for the in-situ nucleation and growth of carbon nanotubes. These form bundles smaller than 100 nm in diameter and several tens of micrometers long. However, the carbon nanotubes-Fe-Al2O3 nanocomposite powders may also contain Fe carbide nanoparticles as well as undesirable thick, short carbon tubes and thick graphene layers covering the Fe/Fe carbide nanoparticles. The influence of the Fe content and the reduction temperature on the composition and micro/nanostructure of the nanocomposite powders have been investigated with the aim of improving both the quantity of nanotubes and the quality of carbon, i. e. a smaller average tube diameter and/or more carbon in tubular form. A higher quantity of carbon nanotubes is obtained using a-Al1.8Fe0.2O3 as starting compound, i. e. the maximum Fe concentration (10 cat.%) allowing to retain the monophase solid solution. A further increase in Fe content provokes a phase partitioning and the formation of a Fe2O3-rich phase which upon reduction produces too large Fe particles. The best carbon quality is obtained with only 5 cat.% Fe (a-Al1.9Fe0.1O3), probably because the surface Fe nanoparticles formed upon reduction are a bit smaller than those formed from a-Al1.8Fe0.2O3, thereby allowing the formation of carbon nanotubes of a smaller diameter. For a given Fe content (≤ 10 cat.%), increasing the reduction temperature favours the quantity of nanotubes because of a higher CH4 sursaturation level in the gas atmosphere, but also provokes a decrease in carbon quality.

Synthesis and characterization of polypyrrole/vanadium pentoxide nanocomposite aerogels

Abstract: Vanadium pentoxide/polypyrrole aerogel (ARG) composites have been synthesized by sol–gel routes, and investigated as cathode materials in Li batteries. The primary method utilized simultaneous polymerisation of pyrrole and vanadium alkoxide precursors. Hydrolysis of VO(OC3H7)3 using pyrrole–water–acetone mixtures yielded monolithic green–black gels with polypyrrole/V ratios ranging from 0.15 to 1.0. Supercritical drying yielded high surface (150–257 m2 g–1) aerogels with densities between 0.1 and 0.2 g cm–3 , that were of sufficient mechanical integrity to allow them to be cut without fracturing. TEM studies of the ARGs show that they are comprised of fibers similar to that of V2O5 ARGs, but with a significantly shorter chain length. The interaction between the polypyrrole (PPy) and V2O5 aerogel in the nanocomposites was probed using IR spectroscopy. Our results suggest that the inorganic and organic components strongly interact during the initial stages, thus perhaps impeding the vanadium condensation process. Hence, the PPy/V2O5 nanocomposites exhibited lower electrical conductivity with increased polypyrrole content. The addition of (NH4)2S2O8 as an oxidizing agent improved the conductivity of the nanocomposites. The deleterious effect of the conductive polymer on the bulk conductivity does not necessarily affect the electrochemical properties of these materials. Nanocomposite materials that were subjected to post-oxidative treatment show enhanced Li insertion capacity compared to the pristine ARG. The physical properties of these ‘nanocomposite aerogels’ are different from ‘microcomposites’ prepared by an alternate route, in which the oxide gel is formed in the presence of a dispersion of preformed micrometer-sized polypyrrole particles.

Nanocomposites of dendritic polymers

Abstract: In the present invention, an inorganic reactant is, or reactants are, localized with respect to a dendritic polymer by physical constraint within or by a non-covalent conjugation to the dendritic polymer. The localized inorganic reactant or reactants is/are subsequently transformed to form a reaction product which is immobilized with respect to the dendritic polymer. This immobilization occurs on a nanoscopic scale as a consequence of the combined effects of structural, chemical and physical changes without having covalent bonds between the product(s) and the dendritic container and results in new compositions of matter called dendritic nanocomposites. The resulting nanocomposite material can be used to produce revolutionary products such as water soluble elemental metals, with specific applications including magnetic resonance imaging, catalytic, magnetic, optical, photolytic and electroactive applications.