Narrow Size Dispersion Research Articles

Liquid Russian Dolls

Applied Physics![Figure][1] CREDIT: ABATE AND WEITZ, SMALL 5 , 10.1002/SMLL.200900569 (2009) Oil and vinegar–based salad dressing is a classic example of an emulsion, wherein the droplets of one fluid are trapped inside the bulk of another. Though techniques exist for making higher-order emulsions (with two or more nested droplet layers), they tend either to be inefficient or else to produce droplets that vary widely in size. Abate and Weitz used lithography to fabricate polydimethylsiloxane devices that can efficiently create uniform distributions of emulsion droplets with up to five nested layers. Single emulsions were prepared using pinned-jet flow focusing—injection of the inner fluid from two side ports into a central stream of outer fluid. To increase the number of emulsion layers, additional injection ports with alternating wettability were added along the length of the flow channel. In order to ensure synchronized droplet formation for triple and higher-order emulsions, the nozzles at each injection port were designed to be slightly narrower than the emulsion arriving from upstream; a new droplet thus formed at the injection port only upon perturbation by an incoming droplet. The droplets exhibited very narrow size dispersity at all orders, as illustrated by their hexagonal packing when confined in two dimensions. small 5 , 10.1002/smll.200900569 (2009). [1]: pending:yes

Preparation of TiO2 Nanocrystallites by Oxidation of Ti−Au(111) Surface Alloy

Ti-Au surface alloy oxidation is used to form nanocrystals of TiO(2) on Au(111). In situ scanning tunneling microscopy (STM) studies show that the approach yields arrays of 8-11 nm wide crystals with relatively narrow size dispersion and uniform crystallography. STM imaging shows that their crystallographic form is rutile with a triangular or hexagonal geometry. Scanning tunneling spectroscopy indicates that the crystals have a well-developed band gap, comparable to that in bulk TiO(2).

Size-controlled one-pot synthesis of fluorescent cadmium sulfide semiconductornanoparticles in an apoferritin cavity

A simple size-controlled synthesis of cadmium sulfide (CdS) nanoparticle (NP) cores in thecavity of apoferritin from horse spleen (HsAFr) was performed by a slow chemical reactionsynthesis and a two-step synthesis protocol. We found that the CdS NP core synthesis wasslow and that premature CdS NP cores were formed in the apoferritin cavity when theconcentration of ammonia water was low. It was proven that the control of theammonia water concentration can govern the CdS NP core synthesis and successfullyproduce size-controlled CdS NP cores with diameters from 4.7 to 7.1 nm with narrowsize dispersion. X-ray powder diffraction (XRD), energy dispersive spectroscopy(EDS) analysis and high-resolution transmission electron microscopy (HR-TEM)observation characterized the CdS NP cores obtained as cubic polycrystalline NPs,which showed photoluminescence with red shifts depending on their diameters.From the research of CdS NP core synthesis in the recombinant apoferritins,the zeta potential of apoferritin is important for the biomineralization of CdSNP cores in the apoferritin cavity. These synthesized CdS NPs with differentphotoluminescence properties will be applicable in a wide variety of nano-applications.

Quantum Dot Nanobarcodes: Epitaxial Assembly of Nanoparticle−Polymer Complexes in Homogeneous Solution

Multiplexed nanobarcodes have been prepared with quantum dots (QDs) and alternating amphiphilic copolymers consisting of hydrocarbons and maleic anhydride groups. In homogeneous solution, the QD-polymer complexes grow epitaxially into nanobeads of narrow size dispersity, which has been previously achieved only for micrometer-sized beads in the presence of solid supports. As a result of this new nanostructure formation mechanism, more than 250 QDs can be loaded into a nanobead of 100 nm in diameter. A model assay for sensitive detection of human prostate specific antigen has also been demonstrated using the QD-nanobeads as fluorescent reporters. This nanoparticle-polymer self-assembly technology is capable of producing a variety of nanostructures and is expected to open new opportunities in nanoparticle-based ultrasensitive detection and imaging.

Metal ion‐imprinted polymer microspheres derived from copper methacrylate for selective separation of heavy metal ions

AbstractMicrobeads of metal ion‐imprinted polymers (MIIPs) were prepared by a novel precipitation polymerization technique, in which copper methacrylate monomer and ethylene glycol dimethacrylate crosslinker were copolymerized in a rotary evaporator. The prepared microbeads had mono‐ or narrow size dispersity, and their sizes increased from 1 to 4 μm with decreasing solvent amount or increasing initiator concentration. The absorption capacity and selectivity of the imprinted polymer for copper ion were determined in the presence of various competitive metal ions. As results, adsorption equilibrium was quickly achieved in about 10 min with high absorbability (about 90%). The effects of pH, initial metallic ion concentration, and MIIP bead size on the absorption capacity were investigated. The Cu(II)‐imprinted polymers exhibited extremely high selectivity, which was much higher than that of corresponding blank polymers. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008

Cylindrical Block Copolymer Micelles and Co-Micelles of Controlled Length and Architecture

Block copolymers consist of two or more chemically different polymers connected by covalent linkages. In solution, repulsion between the blocks leads to a variety of morphologies, which are thermodynamically driven. Polyferrocenyldimethylsilane block copolymers show an unusual propensity to forming cylindrical micelles in solution. We found that the micelle structure grows epitaxially through the addition of more polymer, producing micelles with a narrow size dispersity, in a process analogous to the growth of living polymer. By adding a different block copolymer, we could form co-micelles. We were also able to selectively functionalize different parts of the micelle. Potential applications for these materials include their use in lithographic etch resists, in redox-active templates, and as catalytically active metal nanoparticle precursors.

Structure and Morphology of Annealed Gold Films Galvanically Displaced on the Si(111) Surface

The effects of thermal treatment in ultrahigh vacuum (UHV) of gold films galvanically displaced on the Si(111) surface are studied with low-energy electron diffraction, Auger electron spectroscopy, atomic force microscopy, Kelvin probe force microscopy, and X-ray photoelectron spectroscopy. Annealing the galvanically displaced gold on Si substrates to 1100 K produces films with similar structure, composition, and morphology to annealed gold films evaporated on Si in UHV. The surface morphology is consistent with the Stranski−Krastanov growth mode. Compared to the unannealed film, an interfacial gold silicide layer forms upon annealing, although with limited improvement in adhesion. We report the formation of submicrometer Au/Si islands with narrow size dispersion, separated by deep trenches and with local order and shape dictated by the symmetry of the substrate. A mechanism for the formation of these islands is proposed.

A study of size dependent structure, morphology and luminescence behavior of CdS films on Si substrate

Size tunable cadmium sulfide (CdS) films deposited by a dip coating technique on silicon (100) and indium tin oxide/glass substrates have been characterized using X-ray diffraction, X-ray reflectivity, transmission electron microscopy, atomic force microscopy and photoluminescence spectroscopy. The structural characterization indicated growth of an oriented phase of cadmium sulfide. Transmission electron microscopy used to calculate the particle size indicated narrow size dispersion. The tendency of nanocrystalline CdS films to form ordered clusters of CdS quantum dots on silicon (100) substrate has been revealed by morphological studies using atomic force microscopy. The photoluminescence emission spectroscopy of the cadmium sulfide films has also been investigated. It is shown that the nanocrystalline CdS exhibit intense photoluminescence as compared to the large grained polycrystalline CdS films. The effect of quantum confinement also manifested as a blue shift of photoluminescence emission. It is shown that the observed photoluminescence behavior of CdS is substantially enhanced when the nanocrystallites are assembled on silicon (100) substrate.

Synthesis of magnetite (Fe 3O 4) nanoparticles without surfactants at room temperature

Iron oxide nanoparticles in the interval of 4–43 nm were synthesized by a colloidal method at room temperature, without use of surfactants and using precursors like FeCl 3·6H 2O and FeCl 2·4H 2O; deionizated water free of dissolved oxygen and ammonia solution (29% vol.) and using several aging times (2, 5 and 10 min). A detailed study by X- ray diffraction (XRD), Conventional Transmission Electron Microscopy (CTEM), High-Resolution Transmission Electron Microscopy (HRTEM) and electron diffraction patterns showed that with a reaction time less than 5 min nanoparticles of magnetite phase (Fe 3O 4) were synthesized, and with a bigger time of reaction the lepidocrocite phase (FeO(OH)) was identified. The minor particle average size measured was 6 nm in the sample, 0.0125 M with 2 min of aging time (0.0125M2 m). In addition it was possible to obtain a narrow nanoparticle size dispersion from 4 to 10 nm for small aging times.

Preparation of mesoporous calcium doped silica spheres with narrow size dispersion and their drug loading and degradation behavior

The mesoporous calcium doped silica spheres (CaMS) as well as silica spheres (MS) have been successfully synthesized by a simple one-step method. MS showed a uniform sphere morphology and CaMS exhibited an ellipse morphology with the long axis of around 100 nm. The amount of CaO in CaMS was up to 8.18 wt%. The mesoporous structures of MS and CaMS were studied by X-ray diffraction, transmission electron microscopy and liquid nitrogen adsorption. The results showed that the addition of Ca(NO 3) 2 led to the decreased cell parameters and the increased pore size of CaMS compared to MS. Ibuprofen (IBU) drug storage capacities and release rate were investigated and there was no obvious difference between MS and CaMS. The degradation results showed that CaMS had a significant higher degradation rate than MS. The mesoporous calcium doped silica spheres have potential as drug carrier for controlled-release application.

Targeted nanoparticles for detecting and treating cancer

AbstractEnabled by their size and supramolecular structures, nanoparticles (that is, particles of approximately 10 to 100 nanometers) promise to be particularly capable agents in the detection, diagnosis, and treatment of cancer. When loaded with chemotherapeutic agents, nanoparticle delivery to cancerous tissues relative to healthy tissues may be favorably biased by size and through the attachment of targeting ligands to the surface of the particle. Nanoparticles may be made from a variety of materials, and in addition to chemotherapeutic payloads, nanoparticles can incorporate non‐bioactive elements useful as diagnostic and device agents. For example, the inclusion of iron oxide colloids enables nanoparticle use as magnetic resonance imaging (MRI) contrast agents, and also, through the application of an alternating magnetic field (AMF), enables the particle to generate enough heat to be used for hyperthermic therapeutic applications. In this report, we also introduce novel Magnetic Nanoparticle Hydro‐Gel (MagNaGelTM) materials comprised of chemotherapeutic agents, iron oxide colloids, and targeting ligands. MagNaGel particles were fabricated in the 20‐ to 40‐nm size range with very narrow size dispersion. These particles demonstrate high (>10 wt %) chemotherapeutic loading, tumor‐associated biomolecular binding, good magnetic susceptibility, and attractive toxicity and circulation profiles in mouse models. Looking forward, the convergence of drug and device on the nano‐scale promises treatment modalities that cannot be practiced through traditionally distinct drug and device combinations. MagNaGel nanoparticles are drug‐device hybrids that, when used in conjunction with diagnostic MRI and inductive heating, may play a key role in new and powerful cancer treatment regimens. Drug Dev. Res. 67:70–93, 2006. © 2006 Wiley‐Liss, Inc.

Oxide glass used as inorganic template for fluorescent fluoride nanoparticles synthesis

Abstract We report an original way to synthesise single-crystal PbF 2 nanoparticles by selective chemical attack of a bulk nanocomposite oxyfluoride glass–ceramic. Free of impurities and homogeneously doped with Er 3+ ions, the particles are of narrow size dispersion around 15 nm and weakly aggregated. The nanocrystallites emit a very intense green and blue up conversion fluorescence after infrared excitation. The doping level and the size of the particles is finely driven through the precursor glass–ceramic synthesis and composition.

Synthesis of TiO2 Photocatalysts in Supercritical CO2 via a Non-hydrolytic Route

Nanoscaled TiO2 powders with narrow size dispersion were prepared in supercritical carbon dioxide via non-hydrolytic acylation/deacylation of titanium alkoxide precursors with or without tris-fluorination. The microstructures of these powders were characterized by spectroscopic (FTIR, TGA, and XRD), microscopic (SEM or TEM), and surface area (BET) measurements. Photocatalytic oxidation of 1-octanol on these calcined TiO2 powders and on commercial T805 TiO2 suspended in aerated supercritical carbon dioxide revealed relative reactivity controlled by the powder microstructures. Calcined TiO2 prepared from titanium(IV) isopropoxide and trifluoroacetic anhydride was effectively dispersed in aerated supercritical carbon dioxide under stirring and exhibited high photocatalytic oxidation activity.

Continuous Free-Flow Electrophoresis of Water-Soluble Monolayer-Protected Clusters

There has recently been a surge of interest in the properties and applications of monolayer protected clusters (MPCs). MPCs are metal nanoparticles that have unique optical, chemical, and electrochemical properties resulting from their small size. Because the size defines their properties, MPC particle size fractionation is important for control of the MPC characteristics for use in many potential applications. This paper explores the use of continuous free-flow electrophoresis (CFE) for the size fractionation of N-(2-mercaptopropionyl)glycine (tiopronin) monolayer protected gold clusters into monodisperse nanoparticle samples. CFE is a fractionation technique that isolates monodisperse particle sizes into several different collection vials on the tens of milligrams scale. This allows the MPCs to be separated based on their electrophoretic mobilities into isolated, monodisperse particles across a wide range of sizes. CFE separation of water-soluble tiopronin MPCs yielded fractions that varied in color, UV-visible spectra, transmission electron microscopy (TEM) size histograms, and solubility, indicating narrow size dispersity in the isolated fractions. UV-visible spectrophotometry verified the separation of the tiopronin MPCs through the inspection of surface plasmon resonance peak sizes for the different fractions. TEM was also used to verify the narrowed dispersity of MPC samples. The ability to separate water-soluble nanoparticles into 30 or more fractions in a continuous flow process will enable future studies on their size dependent properties.

Layered MnO2 Nanobelts: Hydrothermal Synthesis and Electrochemical Measurements

A cathode material for rechargeable lithium batteries is one possible application for the birnessite‐related layered MnO2 nanobelts (see Figure) reported here. A simple hydrothermal procedure is described that results in high‐purity, long (up to several tens of micrometers) nanobelts with narrow size dispersion (width 5–15 nm) that are usually self‐assembled into bundles.

Encapsulation of Brewers Yeast in Chitosan Coated Carrageenan Microspheres by Emulsification/Thermal Gelation

Brewers yeast was encapsulated in kappa-carrageenan microspheres using an emulsification-thermal gelation approach. Due to heat sensitivity of the yeast at temperatures in excess of 36 degrees C, mixtures of low and high gelation temperature carrageenans were tested to obtain a blend yielding a gelation temperature under 40 degrees C. A 20:80 dispersion of 2% carrageenan sol containing cells, in warm canola oil, produced microspheres upon cooling, with a mean diameter of 450 microm and narrow size dispersion (span of 1.2). Application of a chitosan membrane coat to minimize cell release, increased the mean microsphere diameter to 700 microm, due to the coat thickness and swelling of the microspheres. This diameter was designed so as to minimize mass transfer limitations. Batch fermentations were carried out in a 3 L reactor on a commercial wort medium. Cell loading was 10(7) cells mL(-1) microspheres, and cell "burst" release was observed upon inoculation into fresh medium, whether microspheres were coated or not. The kinetics of intra- and extracapsular cell growth were determined. Increased concentrations of extracapsular free cells could be accounted for by growth in the wort medium, and by ongoing release from the gel microspheres, whether coated or not. Cell release from chitosan-coated carrageenan microspheres was less than that from uncoated microspheres, likely due to retention by the membrane coat. Growth kinetics and alpha-amino nitrogen consumption of encapsulated yeast were higher than that of free cells, and differences in alcohol and ester profiles were also observed, likely due to modified metabolism of the encapsulated yeast.

Strong carrier confinement and evidence for excited states in self-assembled InAs quantum islands grown on InP(001)

Photoluminescence (PL) and photoluminescence excitation (PLE) experiments are carried out in order to study the electronics states in self-assembled InAs quantum islands (QI's) fabricated on the InP(001) substrate by solid source molecular-beam epitaxy using the Stranski-Krastanov growth mode. The growth conditions of the InAs QI's have been optimized (high growth temperature, low arsenic pressure and growth rate) in order to minimize the island size dispersion. The low-temperature (8 K) PL spectrum of the InAs/InP(001) QI's is characterized by multicomponent transitions. From PLE spectroscopy, we have evidenced excited states associated with a single ground state in agreement with a unimodal size distribution. The full width at half maximum of the ground state PL peak is only 22 meV at 8 K, which reveals a narrow island size dispersion. The integrated PL intensities measured as a function of the temperature have shown a weak intensity decrease between 8 and 300 K. Intensity remains very strong at room temperature, as much as 49% of that at 8 K under nonresonant excitation and up to 90% under quasiresonant excitation. These results are indicating of a strong confinement and/or spatial localization of the carriers in such InAs/InP(001) QI's.

SnO 2 nanocrystals in SiO2: A wide-band-gap quantum-dot system

Nanoclusters of crystalline SnO2 have been grown in glass, starting from tin-doped silica prepared by a sol–gel method. Based upon a particular choice of molecular precursors, nanocrystallites with a mean radius of about 1 nm and a quite narrow size dispersion were obtained, resulting in wide-band-gap (>4 eV) quantum dots (QDs). In this system, differently from other semiconductor-doped glasses, both the glassy host and the nanophase are oxides of IV-group elements. Owing to their thermochemical compatibility, the two phases give stable optical-grade glass ceramics with potential applications in photonics, opening up the field to technological employments of wide-band-gap QDs.

Narrow size-distributed silicon cluster beam generated using a spatiotemporal confined cluster source

We have developed a new laser ablation type cluster source named `spatiotemporal confined cluster source' (SCCS), which gives well-defined thermo-dynamical conditions for cluster growth with narrow size dispersion. A laser-induced shock is controlled to produce a definite mixed gas layer of the silicon vapor and helium gas, which is locally confined in a sub millimeter space, and conserved densely for a time of 160 μs. The generated silicon clusters, which are ionized by an ArF excimer laser for mass analysis without dissociation, show narrow size dispersion with characteristically higher abundance of stable Si 23H x (46%), Si 19H x (14%), and Si 21H x (12%) clusters.

Study on the preparation and properties of styrene–butyl acrylate–silicone copolymer latices

Copolymer latices of styrene–butyl acrylate–silicone were prepared using a semicontinuous addition process and batch and monomer emulsion addition processes. The results showed that a stable latex with narrow particle size dispersion and a high monomer conversion can be obtained only by the semicontinuous addition process. The simultaneous free-radical and ionic copolymerization mechanisms were discussed. 3-Methacryloyloxypropyl trimethoxysilane in this work was used as a coupling agent to form a chemical bond between vinyl polymer and polysiloxane. It was found that the copolymerization reaction and the properties of latex and latex film were obviously influenced by silicone content. When the silicone content was less than 25 wt %, copolymerization proceeded readily and a stable latex could be prepared. With increasing silicone content, monomer conversion, latex stability, film hardness, and tensile strength decreased, whereas the water resistance and impact strength increased. Results of Soxhlet extraction, silicon analysis, and dynamic mechanical properties of latex polymer confirmed the occurrence of copolymerization. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 82: 3194–3200, 2001