Showing papers on "Nanoparticle published in 1995"

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

Crystallization of opals from polydisperse nanoparticles

Abstract: We report the reversible formation of crystals of nanoparticles (opals) from solutions of polydisperse gold nanocrystals. The structures are identified by transmission electron microscopy, and are characterized by hexagonal domains of large particles at the center, surrounded radially by successively smaller particles. Simulated annealing Monte Carlo calculations are used to demonstrate that these configurations correspond to minimization of the mesoscopic van der Waals energy of polydisperse particles, and the driving force for ordering is the size dependence of dispersional attractions.

Theory of 1/T1 and 1/T2 NMRD profiles of solutions of magnetic nanoparticles.

Abstract: Organically coated iron oxide crystallites with diameters of 5-50 nm ("nanoparticles") are potential magnetic resonance imaging contrast agents. 1/T1 and 1/T2 of solvent water protons are increased dramatically by magnetic interactions in the "outer sphere" environment of the nanoparticles; subsequent diffusive mixing distributes this relaxation throughout the solvent. Published theory, valid for the solute magnetic energy small compared with thermal energy, is applicable to small magnetic solutes (e.g., gadolinium and manganese diethylenetriaminopentaacetic acid, and nitroxide free radicals) at generally accessible fields (< or = 50 T). It fails for nanoparticles at fields above approximately 0.05 T, i.e., at most imaging fields. The authors have reformulated outer sphere relaxation theory to incorporate progressive magnetic saturation of solute nanoparticles and, in addition, indicate how to use empirical magnetization data for realistic particles when their magnetic properties are not ideal. It is important to handle the effects of rapid thermally induced reorientation of the magnetization of the nanoparticles (their "superparamagnetism") effectively, including their sensitivity to particle size. The theoretical results are presented as the magnetic field dependence (NMRD profiles) of 1/T1 and 1/T2, normalized to Fe content, for three sizes of particles, and then compared with the limited data extant for well-characterized material.

A fascinating new field in colloid science: small ligand-stabilized metal clusters and possible application in microelectronics

Abstract: Small metal clusters, like Au55(PPh3)12Cl6, which fall in the size regime of 1–2 nm are colloidal nanoparticles with quantum properties in the transitional range between metals and semiconductors. These chemically tailored quantum dots show regarding the Quantum Size Effect (QSE) a level splitting between 20 and 100 meV, increasing from small particle sizes to the molecular state. The organic ligand shell surrounding the cluster acts like a dielectric “spacer” generating capacitances between neighboring clusters down to 10−18 F. Therefore, charging effects superposed by level spacing effects can be observed. The ligand-stabilized colloidal quantum dots in condensed state can be described as a novel kind of artificial solid with extremely narrow mini or hopping bands depending on the chemically adjustable thickness of the ligand shell and its properties. Since its discovery, the Single Electron Tunneling (SET) effect has been recognized to be the fundamental concept for ultimate miniaturization in microelectronics. The controlled transport of charge carriers in arrangements of ligand-stabilized clusters has been observed already at room temperature through Impedance Spectroscopy (IS) and Scanning Tunneling Spectroscopy (STS). This reveals future directions with new concepts for the realization of simple devices for Single Electron Logic (SEL).

Morphology, structure, and growth of nanoparticles produced in a carbon arc.

Abstract: The morphology and crystalline microstructure of carbon-encapsulated nanoparticles produced in a Huffman-Kr\"atschmer fullerene reactor are studied systematically as a function of location within the reactor. X-ray powder diffraction and high-resolution transmission electron microscopy are used to characterize powder harvested from the reactor walls and the inner and outer cores of the cathode deposit. We observe increased graphitization and crystallinity, more faceting, and more gaps between the nanoparticle and the encapsulating carbon cages in the cathode deposit when compared to the wall powder. We propose a growth model based on gas-phase nucleation to explain these observations, linking carbon arc nanoparticle synthesis to existing work on gas aggregation cluster sources.

Synthesis, characterization, and properties of microemulsion-mediated nanophase TiO2 particles

Abstract: Nanophase Ti02 particles, with typical particle sizes in the range of 20-50 nm, have been synthesized using a microemulsion-mediated process. In this process, the aqueous cores ofwater/TritonX-100/exanol/ cyclohexane microemulsions have been used as constrained microreactors for the precipitation of precursor titanium hydroxide. The hydroxide particles thus formed were separated, dried, and calcined at different temperatures to form nanoparticles of TiO2. In order to see the phase transition temperature, thermogravimetric analysisldifferential thermal analysis studies were performed on the precursor hydroxide particles. The average particle size ofthese particles was determined by transmission electron microscopy, BET surface area and line broadening by X-ray diffraction. Phase transformation of these particles was confirmed by X-ray diffraction. The attenuation of ultraviolet radiation increased as the particle size decreased. As a catalyst for the photodegradation ofphenol, only the anatase form ofTiO2 showed significant degradation of phenol, whereas the rutile form of Ti02 was totally inactive for this reaction.

Particle structure control in nanoparticle synthesis from the vapor phase

Abstract: Nanostructured materials have generally been synthesized by condensation from the vapor phase in an inert carrier gas, most often in a buoyant plume above a hot vapor source. Particles form by homogeneous nucleation as the gases cool and grow by Brownian coagulation. Previous studies have shown that the size of the smallest structures is reduced with decreasing pressure, so most nanoparticle synthesis is performed at low pressures. The crystallites produced by this method are subunits of larger agglomerate particles, often with substantial neck formation that interferes with consolidation. Examination of the theory of particle growth under such conditions reveals that, once agglomerate particles begin to form, particle growth rapidly accelerates. The crystallite size is, therefore, determined by the growth prior to the onset of agglomeration. From this analysis, it is seen that the rate of production of nanoparticles can be increased dramatically if the synthesis reactor is operated at higher pressure, with correspondingly shorter growth times. The growth time is determined by the effective cooling rate in the growth region of the reactor. Short growth times are achieved by rapid cooling. Neck formation in those agglomerate particles that do form is diminished by starting the growth process at a high initial temperature.

Nanoparticle formation using a plasma expansion process

Abstract: We describe a process in which nanosize particles with u narrow size distribution are generated by expanding a thermal plasma carrying vapor-phase precursors through a nozzle. The plasma temperature and velocity profiles are characterized by enthalpy probe measurements. by calorimetric energy balances. and by a model of the nozzle flow. Aerosol samples are extracted from the flow downstream of the nozzle by means of a capillary probe interfaced to a two-stage ejection diluter. The diluted aerosol is directed to a scanning electrical mobility spectrometer (SEMS) which provides on-line size distributions down to particle diameters of 4 nmt. We have generated silicon, carbon, and silicon carbide particles with number mean diameters of about 10 not or less, and we have obtained some correlations between the product and the operating conditions. Inspection of the size distributions obtained in the experiments, together with the modeling results, suggests that under our conditions silicon carbide formation is initiated by nucleation of extremely small silicon particles from supersaturated silicon vapor, followed by chemical reactions at the particle surfaces involving carbon-containing species from the gas phase.

Conducting Polyaniline Nanoparticle Blends with Extremely Low Percolation Thresholds

Abstract: Blends of HCl-doped polyaniline (PANI.HCl) nanoparticles with the following conventional polymers, poly(vinyl chloride), polystyrene, poly(methyl methacrylate), poly(vinyl acetate), and poly(vinyl alcohol) (PVA), were prepared by suspending preformed submicronic PANI-HCl particles in the solutions of the matrix polymers and sonicating the suspension for 1.5 h. The submicronic PANI-HCl particles were prepared by oxidative dispersion polymerization using poly(vinyl methyl ether) (PVME) stabilizer. The particles contained 4.4 wt % PVME and had a conductivity of 4.96 S/cm. They had an oblong shape (250 nm×190 nm). Sonication breaks the particles to sizes less than 20 nm. The blend films exhibit an extremly low percolation threshold (f p ) in every case. The volume fraction of PANI-HCl at the percolation threshold for the above mentioned matrices lies in the range 2.5×10 -4 to 4×10 -4 . Transmission electron microscoopy of PANI-HCl-PVA blend films directly cast on carbon-coated TEM grids reveals connectivity at compositions close to f p . Self-assembly of the nanoparticles is evident from the TEM pictures

Preparation and characterization of Fe2O3 nanoparticles in mesoporous silicate

Abstract: Nanoparticles of Fe2O3 are encapsulated into the uniform pores of MCM-41 and the bandgap of the resulting Fe2O3particles is widened from 2.1 to 4.1 eV owing to the quantum size effect.

Manganese doped zinc sulphide nanoparticles by aqueous method

Abstract: Zinc sulphide nanoparticles in the size range ∼10–40 A diameter have been synthesized using the aqueous chemical method. Scanning tunneling microscopy showed that particles are indeed nanosize particles. The size dependent band gap could be varied from a bulk value of 3.68 to 4.5 eV. X‐ray diffraction indicated that nanoparticles are crystalline except for those with band gap ∼4.5±0.1 eV. Nanoparticles with particle size ∼21×2 A diameter or energy gap 4.1×0.1 eV were doped with manganese. The photoluminescence peak at ∼600 nm corresponding to yellow light emission was observed. Atomic absorption studies show that maximum luminescence intensity is achievable with 0.12 at. wt % of Mn doping.

Formation and stabilization of a biodegradable polymeric colloidal suspension of nanoparticles

Abstract: The formation of a colloidal suspension of nanoparticles was obtained, in a very simple manner, by transferring a solution of poly-ɛ-caprolactone in a good solvent (L1) into a non-solvent (L2). Photon Correlation Spectroscopy (PCS) measurements confirmed by microscopic observations were used to determine the morphological aspects of the preparations. The influence of several factors on nanoprecipitation was examined: polymer concentration, L1/L2 ratio, dielectric constant of the final mixture. An experimental model of the phenomenon, which takes into account the flocculation concentration and the L1/L2 ratio, is proposed. It allows the optimal conditions for nanoparticles formation to be determined.

Process for preparing nanoparticles

Abstract: Nanoparticles are prepared by dissolving a poly(ethylene oxide) and/or poly(propylene oxide) polylactic copolymer in an organic solvent followed by formation of nanoparticles by mixing the solution containing the polymer with an aqueous solution and by precipitation, without using an additional colloidal protective agent or by microfluidization and solvent evaporation. Nanoparticles prepared by this method are disclosed.

Method of manufacturing encapsulated doped particles

Abstract: Doped encapsulated semiconductor nanoparticles of a size (<100 Å) which exhibit quantum effects. The nanoparticles are precipitated and coated with a surfactant by precipitation in an organometallic reaction. The luminescence of the particles may be increased by a further UV curing step.

Homogeneous precipitation of doped zinc sulfide nanocrystals for photonic applications

Abstract: A process was developed to prepare nanocrystalline and quantum-confined particles of manganese-doped zinc sulfide. By the reaction of diethylzinc with solubilized hydrogen sulfide, particle sizes of 30–36 A were achieved by control of reactant concentration, and size appeared to vary with the thermodynamic considerations indicative of homogeneous precipitation. Managanese doping required the development of an in situ chemical reaction compatible with the homogeneous precipitation reaction. To that end, ethylmagnesium chloride was reacted with manganese chloride to form the metastable diethylmanganese which acted as the dopant source. Quantum confinement of the particles was accomplished by using methacrylic acid and poly(methyl methacrylate) polymer of low molecular weights. These surfactants were transparent to the ultraviolet wavclcngths of light which allowed luminescent excitation of the material and provided surface passivation which enhanced phosphor brightness. The surfactant adsorption and effect of ultraviolet curing of the surfactant on the luminescent efficiency of the doped nanocrystals was investigated by infrared spectroscopy. These results indicate that the chemisorption of the surfactants to the nanoparticle surface and oxidation followed by crosslinking during curing are responsible for the improvement in luminescent efficiency.

Scanning Tunneling Microscopy, Tunneling Spectroscopy, and Photoelectrochemistry of a Film of Q-CdS Particles Incorporated in a Self-Assembled Monolayer on a Gold Surface

Abstract: Films of AOT-capped (AOT = dioctyl sulfosuccinate) cadmium sulfide nanoparticles (Q-CdS) prepared by incorporation into a self-assembled monolayer (SAM) of hexanethiol on Au were prepared. These were imaged at negative substrate bias in air by scanning tunneling microscopy, and Q-CdS particles were shown to cover most of the area on the SAM. Continuous scanning of the tip over the substrate removed Q-CdS particles to the outside of the scanning area because of tip-substrate interactions. Scanning tunneling spectroscopy was carried out in air with the tip held over the thin CdS film (100 nm) and over individual Q-CdS particles in the layer. The i vs V and dildV vs V curves indicated that the energy band gap of the Q-CdS particles is wider than that of the thin CdS films. The results of photoelectrochemistry also indicated that the onset photopotential is more negative for smaller Q-CdS particles and is related to the level of conduction band.

Structures of nanoparticles prepared from oil-in-water emulsions.

Abstract: Hydrophobic substances were dissolved in an organic solvent and emulsified with an aqueous solution at very high shear. Droplets of very small sizes (50–100 nm) were obtained by using surfactants which were combinations of lecithins and bile salts. After emulsification, the organic solvent was removed by evaporation, yielding stable dispersions of solid particles. The sizes, shapes, and structures of the particles were examined through quasi-elastic light scattering, small-angle neutron scattering and cryotransmission electron microscopy. Cholesteryl acetate particles stabilized by lecithin and bile salts were found to be platelets of 10–20 nm thickness and 80 nm diameter. Cholesteryl acetate particles stabilized with POE-(20)-sorbitan monolaurate were dense spherical globules of diameter 100 nm. Particles with a composition similar to the endogenously occurring lipoprotein, LDL, were large spherical globules studded with small vesicles. The subsequent evolution of the Cholesteryl acetate dispersion upon aging was examined. There was no transfer of cholesteryl acetate between particles nor to large crystals. However, some aggregation of the particles was observed when the volume fraction of the particles in the aqueous dispersion exceeded 0.05. Thus, the structure of the nanoparticles obtained through deswelling of emulsion droplets changes according to the nature of the emulsifiers and to the composition of the hydrophobic substances which they contain.

Preparation of Size-Quantized CdS and ZnS Particles in Nanophase Reactors Provided by Binary Liquids Adsorbed at Layered Silicates

Abstract: Liquid sorption measurements of hexadecylpyridinium montmorillonite (HDPM) dispersions in ethanol (1)-cyclohexane (2) and methanol (1)-cyclohexane (2) binary mixtures established the formation of a 0.5- to 5-nm-thick alcohol (1)-rich adsorption layer at the organoclay complex interfaces. This adsorption layer was used as a nanophase reactor for the in situ generation of size-quantized cadmium sulfide and zinc sulfide semiconductor particles from cadmium (or zinc) acetate and equivalent amounts of H 2 S. The volumes of the nanophase reactor in ethanol (1)-cyclohexane (2) at 1 :2 = 0.05 :99.95 were determined, by adsorption excess isotherm and X-ray diffraction measurements, to be 0.692 cm 3 /(g of HDPM) and 0.746 cm 3 /(g of HDPM), respectively. Adsorption excess isotherm and X-ray diffraction measurements gave corresponding values of 0.170 cm 3 /(g of HDPM) and 0.231 cm 3 /(g of HDPM) in methanol (1)-cyclohexane (2) at 1 :2 = 0.01 :99.99. As expected, smaller sized semiconductor particles were generated in the smaller nanophase reactor, provided by the methanol-rich adsorption layer. Further reduction of semiconductor particles was accomplished by decreasing the concentration of their parent ions in the nanophase reactor. Incorporation of semiconductor nanocrystallites into HDPM manifested themselves in increased viscosity of the suspension. Information on the fractal dimensions of the semiconductor-clay organocomplex suspensions and that on the radius of gyration of the nanoparticles has been determined by small-angle X-ray scattering measurements. The use of selectively adsorbed polar liquids at the solid binary polar-apolar liquid mixture interfaces as versatile nanophase reactors is discussed.

Synthesis of nanosize metallic and alloyed particles in ordered phases

Abstract: Functionalized reverse micelles have been used to synthesize Copper and Cobalt nanoparticles differing by their size and shape. They can be also used to synthesize Fe−Cu alloy (at 30% Fe) and composite (at 70% Fe) particles. In the case of Fe−Cu system, the magnetic properties are presented.

Isolation of ultra small particles

Abstract: The present invention is a method and apparatus for further reducing the size of nanoparticles. Nanoparticles are defined as having an effective average particle size of less than about 400 nm. The present invention separates the nanoparticles further using electric fields.

Method and apparatus for producing high purity and unagglomerated submicron particles

Abstract: A method and apparatus for reacting sodium vapor with gaseous chlorides in a flame to produce nanoscale particles of un-oxidized metals, composites and ceramics. The flame is operated under conditions which lead to condensation of a NaCl by-product onto the particles. The condensate encapsulates the particles and aids in controlling desired particle size and preventing undesirable agglomeration among the particles during synthesis. Following synthesis, oxidation of the particles is inhibited by the encapsulation, and handling character of the products is greatly enhanced. Electron microscopy has revealed that synthesized products are composed of discrete nanoparticles in a NaCl matrix. The NaCl encapsulate has been effectively removed from the particles by both washing and known sublimation technique at 800 °C under low pressure.