Showing papers on "Nanocomposite published in 1995"

Synthesis and barrier properties of poly(ε‐caprolactone)‐layered silicate nanocomposites

Abstract: A new polymer-ceramic nanocomposite has been synthesized consisting of well-dispersed, two-dimensional layers of an organically modified mica-type silicate (MTS) within a degradable poly(e-caprolactone) matrix. A protonated amino acid derivative of MTS was used to promote delamination/dispersion of the host layers and initiate ring-opening polymerization of e-caprolactone monomer, resulting in poly(e-caprolactone) chains that are ionically bound to the silicate layers. The polymer chains can be released from the silicate surface by a reverse ion-exchange reaction and were shown to be spectroscopically similar to pure poly(e-caprolactone). Thick films of the polymer nanocomposite exhibit a significant reduction in water vapor permeability that shows a linear dependence on silicate content. The permeability of nanocomposite containing as low as 4.8% silicate by volume was reduced by nearly an order of magnitude compared to pure poly(e-caprolactone)

Carbon nanotubes as removable templates for metal oxide nanocomposites and nanostructures

Abstract: SEVERAL techniques have been developed recently for fabricating nanocomposite structures by filling1–3 carbon nanotubes4,5. Here we show that surface-tension effects can induce the growth of uniform, thin metal oxide filmsa€"sometimes only a monolayer thicka€"on the outside of nanotubes, along with oxide fillings in the internal cavities and thin oxide layers between the concentric shells of the tubes. We report the preparation of such nanotube–oxide composites by annealing a mixture of partially oxidized nanotubes and V2O5 powder in air above the melting point of the oxide. The external coatings of the tubes are crystalline sheets of the V2O5 layer-like structure, which grow with the c axis parallel to that of the nanotube layers. Intercalation of the oxide occurs where there are missing shells in the nanotubes. We also show that the nanotubes can be partially removed by oxidation, leaving behind layered oxide fibres. Given the importance of vanadium oxides as catalysts and functional ceramics, this role of nanotubes as removable templates might lead to useful new kinds of nanostructured materials.

Nanocomposite materials from latex and cellulose whiskers

Abstract: Composite materials were processed by casting a mixture of aqueous suspensions of latex and microfibrils. These microfibrils, or whiskers, are extracted from a sea animal and are monocrystals of cellulose, with an aspect ratio around 100 and an average diameter of 20 nm. It has been found that the mechanical properties (shear modulus) are increased by more than two orders of magnitude in the rubbery state of the polymeric matrix, when the whisker content was 6% (w/w). This very large effect is discussed on the basis of different types of mechanical models and it is concluded that these whiskers form a rigid network, probably linked by hydrogen bonds. The formation of this network is assumed to be governed by a percolation mechanism.

Hybrid Organic-Inorganic Composites

Abstract: Some General Trends in the Area of Organic-Inorganic Composites Organic-Inorganic Hybrids with a Crystalline Polymer Matrix Inorganic-Protein Interactions in the Synthesis of a Ferrimagnetic Nancomposite Ion-Exchange Intercalation into the MPS[3 Layered Compounds: Design of Nanocomposites with Unusual Magnetic Electrical, and Nonlinear Optical Properties Preparation and Characterization of Nanocomposites of Poly(ethylene oxide) with Layered Solids Polymer-Clay Hybrids (Perfluorosulfonate Ionomer)-(Inorganic Oxide) Nanocomposites: Organic Modification of Surfaces of Silicon Oxide Nanoparticles Grown In Situ Nanostructured Organic-Inorganic Hybrid Materials Synthesized Through Simultaneous Processes Multiple Size Scale Structures in Silica-Siloxane Composites Studied by Small-Angle Scattering Composite Polymer Colloid Nucleated by Functionalized Silica Vinyl-Polymer-Modified Hybrid Materials and Photoacid-Catalyzed Sol-Gel Reactions Hybrid Organic-Inorganic Interpenetrating Networks A New Route to Polymer-Filled Glass: Hybrid Interpenetrating Networks with Appreciable Toughness Solidification of Colloidal Crystals of Silica Thermo-irreversible Gelation and Percolation-Based Mechanical Response via Metal-Olefin Coordination in Diene Polymers Hybrid Organic-Inorganic Silica Materials: Chemical Evidence for Organization in the Solid Hybrid Organic-Inorganic Materials: The Sol-Gel Approach Sol-Gel-Derived Silica-Siloxane Composite Materials: Effect of Reaction Conditions in Polymer-Rich Systems Hypervalent Spiro Polysiliconate and Polygermylate Ionomers: Novel Ladder and Network Materials Hexylene- and Phenylene-Bridged Polysiloxane Network Materials Structural Design of High-Performance Polymers for Sol-Gel Processing Preparation and Properties of High-Clarity Polyamide-Silica Hybrid Materials Preparation and Mechanical Properties of Polybenzoxazole-Silica Hybrid Materials Morphological Studies of Conductive Polyemers Deposited onto High-T[c Superconductors Novel Organic-Inorganic Composite Materials for Photonics Inorganic-Organic Hybrid Coatings for Metals and Glass Surfaces Surface Modification of Carbon Fibers for Advanced Composite Materials

Electroactive and Photoactive Rod-Coil Copolymers: Design, Synthesis, and Supramolecular Regulation of Photophysical Properties

Abstract: : Two series of electroactive and photoactive rod-coil copolymers have been designed, synthesized, and investigated to explore a new structural motif for organizing molecular and macromolecular materials at the supramolecular structure level for enhanced functional and solid state photophysical properties. The rod-coil copolymers consisting of electroactive and photoactive rodlike conjugated segments and inactive coillike segments, exemplified by poly(1,4-phenylene benzobi sthiazole-co-decamethylene benzobisthiazole) and poly( 1 ,4-phenylenebisvinylene benzobisthiazole-co-decamethylene benzobisthiazole), have semi-flexible (semi-rigid) chains whose flexibility (rigidity), folding, intermolecular interactions, and packing, and hence the solid state supramolecular structure and photophysical properties of the materials, are regulated by copolymer composition. The molecular structure, chain sequence lengths, and copolymer composition were determined by NMR (1H, 13C), FTIR, and UV-Visible spectra. The sequence length distribution of the conjugated rodlike segments predicted from the copolymerization statistics was in good agreement with the 1H NMR results. It is shown that nanocomposites are formed at rod molar fractions of less than 0.5 which also marks a dramatic change in the photophysical properties of the copolymers. The photoluminescence quantum yield varied with copolymer composition, reaching over 6- and 7-fold enhancements compared to the "bulk" pure conjugated polymers. jg

Zeta Potential Measurements on Conducting Polymer-Inorganic Oxide Nanocomposite Particles

Abstract: We describe some of our recent results on the characterization of aqueous colloidal dispersions of conducting polymer-inorganic oxide nanocomposite particles. Such colloids are easily prepared by synthesizing the conducting polymer in the presence of commercially available ultrafine silica (or tin(IV) oxide) particles in aqueous media. In the present study we present electrokinetic data as a function of pH for the following systems: polypyrrole-silica, carboxylic acid-functionalized polypyrrole-silica, amine-functionalized polypyrrole-silica, polyaniline-silica, and polypyrrole-tin(IV) oxide colloids. These data show that both the isoelectric points and zeta potentials of these nanocomposite dispersions are governed primarily by the nature of the charged groups at the inorganic oxide surface rather than by the conducting polymer component. This suggests that the inorganic oxide is the major component at the particle surface, which is consistent with the excellent long-term colloid stability of these dispersions. The aqueous electrophoresis measurements also indicate that our surface functionalization experiments were successful: Carboxylic acid groups can be incorporated via copolymerization using an appropriate functional pyrrole comonomer, while amine groups can be introduced via derivatization of the silica component using 3-aminopropyl triethoxysilane.

Electron behavior and magnetic properties of polymer nanocomposites

Abstract: In this review article, an attempt has been made to describe the relatively new class of composite systems, polymer nanocomposites. The study of nanocomposites is determined by a number of anomalous properties, exhibited by both the nanoparticles themselves and the systems of such objects immersed in a polymer matrix.

Surface characterization of conducting polymer-silica nanocomposites by X-ray photoelectron spectroscopy

Abstract: The surface characterization of a range of conducting polymer-silica colloidal nanocomposites by X-ray photoelectron spectroscopy (XPS) is described. The silicon atoms in the silica component and the nitrogen atoms in the conducting polymer (polypyrrole or polyaniline) component have been utilized as unique elemental markers. Thus, measurement of the silicon/nitrogen atomic ratio by XPS allows a semiquantitative assessment of the silica/conducting polymer surface composition of the nanocomposite particles. These surface atomic ratios were then compared with the bulk silicon/nitrogen atomic ratios calculated for the nanocomposites from our macroscopic chemical composition data. We were able to confirm that, for all samples investigated, the surface composition of the conducting polymer- silica particles is silica-rich with respect to their bulk composition. These observations are consistent with the observed long-term colloidal stability ofthese dispersions. Furthermore, the surface composition of the polypyrrole-silica nanocomposites was correlated with the colloid stability of these dispersions in pH 3 and 9 buffer solutions. Finally, our XPs data confirm that, although somewhat depleted from the surface ofthe particles, the conducting polymer component is nevertheless present. This observation is consistent with the relatively high solid state electrical conductivities obtained for compressed pellets of these materials.

Processing and hardness of electrodeposited Ni/Al2O3 nanocomposites

Abstract: Nanocomposite Ni/Al2O3 films have been produced by electrochemical deposition where 50 and 300 nm Al2O3 particles are dispersed in a nickel matrix. These films exhibit considerable enhancements in their hardness in comparison to pure nickel. The strengthening mechanism is explained in terms of an Orowan bowing hardening mechanism and, hence, related to the volume fraction of the reinforcing phase. These films may have application as strong coatings that retain many of the physical properties (e.g., optical, thermal, electrical) of the metal.

Erosion resistant diamond-like nanocomposite coatings for optical components

Abstract: An erosion resistant coating for optically transmissive substrates formed from a diamond-like nanocomposite structure which contains interpenetrating networks of a diamond-like carbon matrix stabilized by hydrogen, a silicone glass-like network stabilized by oxygen, and optionally, at least one network formed from elements and compounds from groups 1-7b and 8 of the periodic table.

Diamond-like nanocomposite corrosion resistant coatings

Abstract: A method for inhibiting corrosion of a substrate by applying to a substrate a corrosion resistant coating comprising a diamond-like solid state material having interpenetrating atomic scale networks of class of diamond-like solid state materials formed from interpenetrating networks comprising a first network of carbon in a diamond-like carbon network stabilized by hydrogen, a silicon network stabilized by oxygen, and optionally at least one network made from dopant elements or dopant compounds containing elements from groups 1-7b and 8 of the periodic table.

Processing of Silicon Carbide‐Mullite‐Alumina Nanocomposites

Abstract: Nanocomposite materials in the form of nanometer-sized second-phase particles dispersed in a ceramic matrix have been shown to display enhanced mechanical properties. In spite of this potential, processing methodologies to produce these nanocomposites are not well established. In this paper, we describe a new method for processing SiC-mullite-Al2O3 nanocomposites by the reaction sintering of green compacts prepared by colloidal consolidation of a mixture of SiC and Al2O3 powders. In this method, the surface of the SiC particles was first oxidized to produce silicon oxide and to reduce the core of the SiC particles to nanometer size. Next, the surface silicon oxide was reacted with alumina to produce mullite. This process results in particles with two kinds of morphologies: nanometer-sized SiC particles that are distributed in the mullite phase and mullite whiskers in the SiC phase. Both particle types are immersed in an Al2O3 matrix.

Method for preserving precision edges using diamond-like nanocomposite film coatings

Abstract: A method for preserving the precision-edges of a precision-edged substrate by applying to a the substrate a corrosion resistant coating comprising a diamond-like solid state material having interpenetrating atomic scale networks comprising a first diamond-like carbon network stabilized by hydrogen, a silicon network stabilized by oxygen, and optionally at least one network made from dopant elements or dopant compounds containing elements from Groups 1-7b and 8 of the periodic table.

Clay-reinforced epoxy nanocomposites: Synthesis, properties and mechanism of formation

Abstract: Smectite clays are promising materials for the preparation of nanostructured polymer-clay composites by in situ intragallery polymerization. In the present work epoxy-clay nanocomposites have been synthesized by the exfoliation of organoclays during the epoxy thermosetting process. The extent of silicate layer separation is governed by the chain length of gallery cations, the clay layer charge density and the acidity of the gallery cations. By using different curing agents, we obtained both glassy and rubbery epoxy matrices. We have quantitatively described the mechanical reinforcement provided by the exfoliated clay layers in both types of matrices. Reinforcement was substantially greater for the rubbery epoxy matrix. Both the tensile strength and the modulus of the nanocomposite increased with increasing clay content. The reinforcement provided by the silicate layers at 15 wt% loading was manifested by a more than ten-fold improvement in tensile strength. The rubbery state of the matrix may allow alignment of the exfoliated silicate layers upon applying strain, thereby enhancing reinforcement.

Incorporation of pyrene into an oriented transparent film of layered silica-hexadecyltrimethylammonium bromide nanocomposite

Abstract: A layered silica-hexadecyltrimethylammonium halide nanocomposite was used as a novel transparent support to immobilize pyrene. For the incorporation of pyrene into the layered composites, pyrene was first solubilized into an aqueous solution of hexadecyltrimethylammonium halide and the solution was allowed to react with partially hydrolyzed tetramethoxysilane. By spin coating the solution on a quartz substrate, thin films were obtained. The films are transparent in a wavelength region from the visible to the near-infrared regions and possessed a layered structure. Fluorescence spectra of the incorporated pyrene suggest that the pyrene molecules were incorporated in the hydrophobic part of the layered composites without aggregation. The present system is a novel state of surfactant aggregates. Applications such as the immobilization of guest species (especially photoactive ones) are promising because of the simplicity of preparation, the micro- and macroscopic anisotropy, and transparency of these layered composites.

Synthesis and properties of a new (PEO)x[Na(H2O)]0.25MoO3 nanocomposite

Abstract: Mono- and bi-layers of polyethylene oxide (PEO) have been incorporated into the interlayer gap of AxMoO3, to give ordered (PEO)x[Na(H2O)n]0.25MoO3 nanocomposites (x= 0.40, mono-; or 0.90, bi-) with interlayer distances of 12.9 and 15 A, respectively. The driving force for the insertion reaction arises from the solvation of the cations by the PEO, together with the increase in entropy resulting from displacement of water molecules from the interlamellar region. We propose a model for the structure of the monolayer and bilayer composites based on X-ray diffraction, 13C/23Na solid-state NMR and IR data. We have carried out a preliminary comparative study of the electrochemical insertion of lithium into the two polymer nanocomposites by using the materials as cathodes in rechargeable lithium batteries. Li can be reversibly inserted into both materials. Lithium ion transport is substantially enhanced in the bilayer nanocomposite as a result of PEO incorporation, compared with the monolayer nanocomposite. The monolayer composite also shows a pronounced decrease in cell capacity on cycling by comparison to the bilayer.