Showing papers on "Nanocomposite published in 1996"

Polymer Layered Silicate Nanocomposites

Abstract: Polymer nanocomposites with layered silicates as the inorganic phase (reinforcement) are discussed. The materials design and synthesis rely on the ability of layered silicates to intercalate in the galleries between their layers a wide range of monomers and polymers. Special emphasis is placed on a new, versatile and environmentally benign synthesis approach by polymer melt intercalation. In contrast to in-situ polymerization and solution intercalation, melt intercalation involves mixing the layered silicate with the polymer and heating the mixture above the softening point of the polymer. Compatibility with various polymers is accomplished by derivatizing the silicates with alkyl ammonium cations via an ion exchange reaction. By fine-tuning the surface characteristics nanodispersion (i. e. intercalation or delamination) can be accomplished. The resulting polymer layered silicate (PLS) nanocomposites exhibit properties dramatically different from their more conventional counterparts. For example, PLS nanocomposites can attain a particular degree of stiffness, strength and barrier properties with far less inorganic content than comparable glass- or mineral reinforced polymers and, therefore, they are far lighter in weight. In addition, PLS nanocomposites exhibit significant increase in thermal stability as well as self-extinguishing characteristics. The combination of improved properties, convenient processing and low cost has already led to a few commercial applications with more currently under development.

Biomimetic Pathways for Assembling Inorganic Thin Films

Abstract: Living organisms construct various forms of laminated nanocomposites through directed nucleation and growth of inorganics at self-assembled organic templates at temperatures below 100°C and in aqueous solutions. Recent research has focused on the use of functionalized organic surfaces to form continuous thin films of single-phase ceramics. Continuous thin films of mesostructured silicates have also been formed on hydrophobic and hydrophilic surfaces through a two-step mechanism. First, under acidic conditions, surfactant micellar structures are self-assembled at the solid/liquid interface, and second, inorganic precursors condense to form an inorganic-organic nanocomposite. Epitaxial coordination of adsorbed surfactant tubules is observed on mica and graphite substrates, whereas a random arrangement is observed on amorphous silica. The ability to process ceramic-organic nanocomposite films by these methods provides new technological opportunities.

Thermoplastic nanocomposites filled with wheat straw cellulose whiskers. Part I: Processing and mechanical behavior

Abstract: Cellulose microcrystals with dimensions of ∼5 nm x 150-300 nm were obtained from wheat straw. To evaluate the reinforcing effect of these fillers within a thermoplastic matrix, composites with a weight fraction of cellulose ranging from 0 to 30 wt% were processed by freeze-drying and molding a mixture of aqueous suspensions of microcrystals and poly(styrene-co-butyl acrylate) latex. It was found that these microcrystals, or whiskers, bring a great reinforcing effect at temperatures higher than the glass transition temperature (T g ) of the matrix and improve the thermal stability of the composite. The relaxed modulus increased continuously with the filler content, and for a film containing 30 wt% of whiskers, it was more than a thousand times higher than that of the matrix. This effect is discussed with regard to theoretical calculations based on a mean field approach (Halpin-Kardos model). It is concluded that the great reinforcement observed seems to be due not only to the geometry and stiffness of the straw cellulose whiskers but also to the interactions of the microcrystals, their topological arrangement, and the probable formation of whisker clusters within the thermoplastic matrix, the cellulose fillers probably being linked through hydrogen bonds.

Intercalates and exfoliates formed with oligomers and polymers and composite materials containing same

Abstract: Nanocomposites are manufactured by combining a host material, such as an organic solvent or a matrix polymer and exfoliated intercalates formed by contacting a phyllosilicate with a polymer to adsorb or intercalate the polymer between adjacent phyllosilicate platelets. Sufficient polymer is adsorbed between adjacent phyllosilicate platelets to expand the adjacent platelets to a spacing of at least about 5 A, preferably at least about 10 A (as measured after water removal), up to about 100 A and preferably in the range of about 30-40 A, so that the intercalate easily can be exfoliated, e.g., when mixed with an organic solvent or a polymer melt, to provide a carrier material for drugs and the like, or to provide a matrix polymer/platelet composite (nanocomposite) material - the platelets being exfoliated from the intercalate.

Concurrent Polymerization and Insertion of Aniline in Molybdenum Trioxide: Formation and Properties of a [Poly(aniline)]0.24MoO3 Nanocomposite

Abstract: We have developed a novel nanocomposite material, [PANI]0.24MoO3, comprised of poly(aniline) chains interleaved with the layers of MoO3, using concomitant ion exchange−polymerization in the presence of an external oxidizing agent. The characterization of this material using SEM, FTIR spectroscopy, powder XRD, and thermal analysis shows that the poly(aniline) is present primarily in the emeraldine salt form. The high degree of ordering evident from the oriented film XRD patterns suggests that the PANI chains are at least partially aligned in the ac (basal) plane. The properties of the polymer nanocomposite for electrochemical lithium insertion were compared to those of the alkali molybdenum oxide using the materials as cathodes in conventional lithium cells. The polymer/oxide battery demonstrated substantially reduced cell polarization on galvanostatic cycling, compared to the alkali molybdenum oxide in the absence of PANI. The resultant enhanced ion and/or electron transport induced by incorporation of th...

Tensile behavior of nanocomposites from latex and cellulose whiskers

Abstract: Cellulose whiskers have been used as reinforcement in a copolymer matrix prepared from a latex phase. If a water suspension-mixing procedure is adopted, the fibril breakage that usually occurs during the mixing with a molten polymer can be avoided, and an enhanced filler dispersion can be expected. In this study, different processing methods have been used to prepare composite films, either by film casting (water evaporation) or by freeze drying, followed by classical compression or extrusion processes. The thermomechanical properties of these nanocomposites have been investigated, and the influence of processing conditions and the effect of whisker content have been considered. Processing conditions have a large influence on the mechanical behavior and can be classified in ascending order of their reinforcement efficiency : It can be attributed to a decrease of the apparent whisker aspect ratio, due to gradual breakage and/or orientation of the whiskers when hot pressing or extrusion is used. Below T g , good agreement is found between experimental moduli and the theoretical predictions of the Halpin-Kardos equation. On the other hand, above T g , a spectacular reinforcing effect is observed, which is widely underestimated by this short fiber composite model. This is related to the presence of a rigid cellulose network, linked by hydrogen bonds, when the whisker content is above its percolation threshold. The quality of this network (i.e., density and homogeneity) and thus, the magnitude of the reinforcing effect, depend on processing conditions.

New Nanocomposite Materials: Microcrystalline Starch Reinforced Thermoplastic

Abstract: New nanocomposite materials consisting of microcrystals obtained from potato starch dispersed in a synthetic polymer matrix were prepared by freeze-drying and molding a mixture of aqueous suspensions of starch microcrystals and thermoplastic polymer latex with a weight fraction of microcrystals ranging from 0 to 60%. It was found that this filler brings a great reinforcing effect, especially at temperatures higher than the T g of the synthetic matrix

Nanocomposites Prepared by Threading Polymer Chains through Zeolites, Mesoporous Silica, or Silica Nanotubes

Abstract: The purpose of this brief review is to describe some recent, preliminary attempts to prepare nanocomposites in which polymer chains thread through the cavities or channels of several types of inorganic materials, specifically zeolites, a mesoporous hexagonal form of silica, and silica nanotubes. One goal is to determine the effects of the constraining geometry on the properties of the chains, in particular, their glass transition temperatures. Another is the hope that this molecular threading will provide such intimate interactions between the polymer chains and their inorganic environment that novel reinforcement effects will be obtained.

Nanocomposite materials (LAW392)

Abstract: The present invention relates to a latex comprising water and a layered material intercalated with a polymer. The invention also relates to a nanocomposite material comprising a layered material intercalated with a polymer. The latex can be produced by forming a dispersion of layered material in water, adding surfactant, polymerizable monomer or monomers, and a polymerization initiator to the mixture and then polymerizing the monomer to form a latex. The latex can also be formed from preformed polymers. Composite materials formed from latexes produced by either method have improved mechanical properties and reduced air permeability.

Synthesis, Structure, and Reactions of Poly(ethylene oxide)/V2O5 Intercalative Nanocomposites

Abstract: The intercalation of poly(ethylene oxide) (PEO) in layered V2O5 xerogel and the structural and physicochemical characterization of the products is reported. The synthesis of PEO/V2O5 nanocomposites is achieved by simply mixing aqueous solutions of PEO with aqueous V2O5 gels followed by slow water evaporation. Several different phases of PEO/V2O5 composites can be obtained by varying the component ratios. The interlayer distance of (PEO)xV2O5·nH2O varies from 13.2 A, at x = 0.5, to 16.8 A at x = 1.0, to 17.6 A at 1 < x < 3, and to 18.3 A at x ≥ 3. One-dimensional electron density calculations based on X-ray diffraction data (perpendicular to layers) show that the composites contain a monolayer of PEO molecules when x < 1 and a bilayer when x ≥ 1. The data suggest that the PEO chains are arranged side-by-side in a fully extended conformation between the layers forming corrugated mono- or bilayers. The (PEO)xV2O5·nH2O intercalation compounds are water swellable and light-sensitive. UV irradiation causes dram...

Magnetic iron oxide–silica nanocomposites. Synthesis and characterization

Abstract: Composite materials containing nanoparticles of maghaemite (γ-Fe2O3) dispersed in a silica matrix have been made by polymerizing a silica precursor (triethoxysilane or silicic acid) inside an aqueous sol of maghaemite particles. After gelation, the examination of xerogels by electron microscopy does not reveal noticeable aggregation of particles. The structure and composition of the silica matrices were deduced from 29Si MAS NMR spectroscopy. Thermal analysis, FTIR and NIR spectroscopic studies showed that the particles and silanol groups of the matrix remain solvated in the composite materials. No Si–O–Fe bonds are formed in the xerogels and the dispersion of particles in the matrix seems to result from the mutual solvation of particle surfaces and remaining silanol groups, as indicated by strongly associated hydrogen-bonded water molecules.

Nonlinear optical properties of nanocomposite materials

Abstract: This paper reviews some of the authors' recent research aimed at obtaining an understanding of the physical processes that determine the linear and nonlinear optical properties of nanocomposite materials. One result of this research is the prediction and experimental verification that under proper conditions two materials can be combined in such a manner that the nonlinear susceptibility of the composite exceeds those of the constituent materials. This paper also presents a survey of the various geometrical structures of composite materials. A common approach to the development of nonlinear optical materials entails searching for materials that possess, at the molecular level, desirable nonlinear optical properties. An alternative approach, which will be explored in this paper, entails combining known materials into a composite material. Under proper conditions, this composite material might combine the more desirable properties of the starting materials, or ideally, might possess properties superior to those of the starting materials. Some of the commonly encountered structures of composite materials are shown in figure 1. The Maxwell Garnett (1) geometry consists of small inclusion particles embedded in a host material. The Bruggeman (2) geometry consists of two intermixed components. These two model geometries are the structures most often encountered in theoretical discussions of composite materials. Two additional structures are that of porous silicon and that of layered materials. Recent research (3) has shown that an electrochemical etching procedure can be used to turn silicon into a porous structure. The resulting structure then contains 'worm holes' which can be modelled as cylindrical columns in which the silicon has been eaten away from the host material. When still more material has been eaten away, the resulting structure can be modelled as cylindrical columns of silicon surrounded by voids. In either case, the voids can be filled with a second material to form a composite structure. These composite materials can be thought of as a two-dimensional version of the Maxwell Garnett structure. Research on porous silicon is still quite new and will not be discussed further in this paper. The final structure illustrated in figure 1 is the layered geometry, consisting of alternating layers of two materials with different linear and nonlinear optical properties. In all of the structures shown in figure 1, we assume that the two materials are intermixed on a distance scale much smaller than an optical wavelength. Under these conditions, the propagation of light can be described by effective values of the optical constants that are obtained by performing a suitable volume average of the local optical response of the material. In fact, performing such an average can be rather subtle for situations involving the nonlinear optical response, because it is the nonlinear polarization that must be averaged, and the nonlinear polarization depends on the spatially inhomogeneous electric field amplitude

Preparation and Characterization of Nanocomposite Thin Films for Optical Devices

Abstract: The incorporation of nanosized inorganic particles into a polymeric matrix represents one of the most difficult problems in the fabrication of nanocomposites. The success in the manufacturing of such materials can be achieved only if the aggregation of particles is avoided, which is essential when high transparency is required, as for optical device applications. Here, a method is described for the preparation of a polymeric nanocomposite, containing a well-dispersed red pigment synthesized by adsorption of an organic dye onto nanosized titania particles. The system can be easily deposited on glass plates by spin coating, yielding homogeneous, low-defect thin films of high color purity and transparency, which can be used as color filters for liquid crystal displays. These films were characterized by scanning electron microscopy and UV/vis spectrophotometry, and their mechanical properties were evaluated by studying the damage induced from ultrasound.

Subnanometer-Diameter Wires Isolated in a Polymer Matrix by Fast Polymerization

Abstract: The preparation and analysis of inorganic-organic polymer nanocomposites consisting of inorganic nanowires and multiwire "cables" in a random-coil organic polymer host is reported. Dissolution of inorganic (LiMo3Se3)n wires in a strongly coordinating monomer, vinylene carbonate, and the use of a rapid polymerization in the presence of a cross-linking agent produce nanocomposites without phase separation. Polymerization of dilute solutions yields a material containing mostly (Mo3Se3(-))n mono- and biwires, 6 to 20 angstroms in diameter and 50 to 100 nanometers long. Polymerization of more concentrated liquid crystalline solutions yields a nanocomposite containing oriented multiwire cables, 20 to 40 angstroms in diameter and up to 1500 nanometers long, that display optical anisotropy and electrical conductivity.

Polymerization of Silicates in Layered Double Hydroxides

Abstract: Layered double hydroxides containing silicate anions have been prepared using either a coprecipitation method or an anionic exchange reaction. The polymerization of the intercalated anions under moderate thermal treatment has been studied by PXRD, FTIR, and solid-state NMR. Grafting processes and layer condensation have been obtained leading to the preparation of new nanocomposite materials with improved physicochemical properties.

Nanostructured Inorganically Pillared Layered Metal(IV) Phosphates

Abstract: This article reviews the synthesis, characterization and ion-exchange, ion-transport, sorptive, and catalytic properties of inorganically pillared layered metal(IV) phosphates, typified by Zr(HPO4)2‚H2O. Porous nanostructures are generally prepared from metal(IV) phosphates either by ion exchange of polynuclear species or by intercalation from solutions of condensed species obtained by the hydrolysis of organometallic precursors using sol-gel methods, followed by thermal treatment to eliminate organic moieties, condense hydroxyl groups, eliminate water, and consolidate the structure by grafting the pillar to the layer. The different strategies devised to overcome the problem presented by the high layer charge density of R- and A-structured phosphates in obtaining porous solids, including exfoliation and local surface growth of pillaring ions, and modification of the zirconium phosphate matrix to reduce the cation-exchange capacity, are described. Structural and textural characteristics of Al, Cr, mixed Al-Cr, Fe-Cr, Ga-Al and of Si-pillared phosphates obtained from XAFS, XPS, and MAS NMR are presented, and the perspectives of nanocomposite pillared layered solids in general are discussed in the current context of mesoporous solids synthesized using templating routes.

Tailoring of thermomechanical properties of thermoplastic nanocomposites by surface modification of nanoscale silica particles

Abstract: Thermoplastic nanocomposites based on linear polymethacrylates as matrix materials and spherical silica particles as fillers have been synthesized using the in situ free radical polymerization technique of methacrylate monomers in presence of specially functionalized SiO2 nanoparticulate fillers. Uncoated monodisperse silica particles with particle sizes 100 nm and 10 nm were used as reference fillers. For surface modification, the alcoholic dispersions of the fillers were treated with appropriate amounts of methacryloxypropyltrimethoxysilane (MPTS) and acetoxypropyltrimethoxysilane (APTS). Transmission electron microscopy (TEM) was used to investigate dispersion behaviour in dependence on surface modification. Dynamic mechanical properties were measured by dynamic mechanical thermal analysis (DMTA).

Capacitive thin films using diamond-like nanocomposite materials

Abstract: A method of making capacitors (25) comprising, providing as the dielectric (27) and/or conductive layers (26), a material made from a diamond-like nanocomposite solid-state material having interpenetrating atomic scale networks of carbon in a diamond-like carbon network stabilized by hydrogen, a glass-like silicon network stabilized by oxygen, and optionally at least one additional network of dopant elements or dopant compounds having elements from Groups 1-7b and 8 of the periodic table.

Pore Structure of Carbon−Mineral Nanocomposites and Derived Carbons Obtained by Template Carbonization

Abstract: The lithium form of taeniolite, intercalated with hydroxyaluminum and hydroxyaluminum−zirconium cations, served as the molecular template for carbon−mineral nanocomposites and derived carbons. The ...

Magnetic nanocompass compositions and processes for making and using

Abstract: A magnetic composition comprising nanocomposite particles comprising from about 0.001 to about 60 weight percent of magnetic nanocrystalline particles dispersed in from about 40 to about 99.999 weight percent of a discrete phase matrix, and a continuous phase matrix, wherein the discrete phase resides in interstices within the continuous phase matrix.