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Colloidal Dispersions (colloidal + dispersion)

Distribution by Scientific Domains

Polymers and Materials Science	75%
Chemistry	20%

Distribution within Polymers and Materials Science

General & Introductory Materials Science	60%
Polymer Science & Technology General	40%

Selected Abstracts

Plasma Nanoparticle Synthesis: Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Mater.
The cover picture shows a view into the plasma zone of a microwave plasma reactor, which is used to synthesize macroscopic quantities of single crystalline silicon nanoparticles with a very high production rate. These nanoparticles exhibit bright luminescence across the visible spectrum. On page 696, the authors report that the emission of such silicon nanoparticles can be tuned by changing their size and surface chemistry. [source]

Luminescent Colloidal Dispersion of Silicon Quantum Dots from Microwave Plasma Synthesis: Exploring the Photoluminescence Behavior Across the Visible Spectrum

ADVANCED FUNCTIONAL MATERIALS, Issue 5 2009
Anoop Gupta
Abstract Aiming for a more practical route to highly stable visible photoluminescence (PL) from silicon, a novel approach to produce luminescent silicon nanoparticles (Si-NPs) is developed. Single crystalline Si-NPs are synthesized by pyrolysis of silane (SiH4) in a microwave plasma reactor at very high production rates (0.1,10,g,h,1). The emission wavelength of the Si-NPs is controlled by etching them in a mixture of hydrofluoric acid and nitric acid. Emission across the entire visible spectrum is obtained by varying the etching time. It is observed that the air oxidation of the etched Si-NPs profoundly affects their optical properties, and causes their emission to blue-shift and diminish in intensity with time. Modification of the silicon surface by UV-induced hydrosilylation also causes a shift in the spectrum. The nature of the shift (red/blue) is dependent on the emission wavelength of the etched Si-NPs. In addition, the amount of shift depends on the type of organic ligand on the silicon surface and the UV exposure time. The surface modification of Si-NPs with different alkenes results in highly stable PL and allows their dispersion in a variety of organic solvents. This method of producing macroscopic quantities of Si-NPs with very high PL stability opens new avenues to applications of silicon quantum dots in optoelectronic and biological fields, and paves the way towards their commercialization. [source]

Tailoring the Flow Properties of Soft Colloidal Dispersions

MACROMOLECULAR SYMPOSIA, Issue 1 2005
Michel Cloitre
Abstract Summary: The dynamics and the non-linear rheology of concentrated dispersions of soft particles are shown to exhibit generic properties. They display both solid-like and liquid-like properties depending on the applied stress. Below the yield point, dispersions exhibit history-dependent phenomena that have all the hallmarks of ageing in glasses. The close-packed disordered structures of the dispersions lie at the heart of this behaviour. Other properties such as the propensity of pastes to slip on solid surfaces appear to be governed by specific contact interactions between the squeezed particles. [source]

Efficient Simulations of Charged Colloidal Dispersions: A Density Functional Approach

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 4 2005
Kang Kim
Abstract Summary: A numerical method is presented for simulating charged colloidal dispersions in electrolyte solutions. Utilizing a smoothed profile for colloid-solvent boundaries, efficient mesoscopic simulations are enabled for modeling dispersions of many colloidal particles exhibiting many-body electrostatic interactions. The validity of the method was examined for simple colloid geometries, and the efficiency was demonstrated by calculating stable structures of two-dimensional dispersions, which resulted in the formation of colloidal crystals. Formation of a charged colloidal crystal. [source]

Effect of Solvation Film on the Viscosity of Colloidal Dispersions

CHINESE JOURNAL OF CHEMISTRY, Issue 5 2005
Peng Chang-Sheng
Abstract Viscosity is one of the most important properties of colloids in mixing, transportation, stabilization, energy consumption, and so on. According to Einstein's viscosity equation, the viscosity of a colloidal dispersion increases with the increase of particle concentration. And the equation can be applicable to all micro-particle dispersions, because the effect of solvation films coated on particles can be neglectable in that case. But with the decrease of particle size to nano-scale, the formation of solvation films on nano-particles can greatly affect the viscosity of a dispersion, and Einstein's equation may not be applicable to this case. In this work, one kind of micro-size silica particle and two kinds of nano-size silica particles were used to investigate the effect of solvation films on dispersion viscosity, dispersed in water and ethyl alcohol solvents, respectively. The results of theoretical calculation and experimental investigation show that the increase of viscosity is contributed from solvation films by more than 95 percent for nano-particle dispersions, while less than 10 percent for micro-particle dispersions. [source]

Inorganic Macroporous Films from Preformed Nanoparticles and Membrane Templates: Synthesis and Investigation of Photocatalytic and Photoelectrochemical Properties,

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2003
D.G. Shchukin
Abstract Colloidal dispersions of titania, zirconia, tin oxide, indium oxide, and ceria have been successfully used to impregnate membrane templates and form the respective metal oxide (MO) porous films. The use of alumina and iron oxide sols in the same procedure, however, resulted in compact structures. By mixing different nanoparticle solutions before impregnation, final inorganic films containing two metal oxides, of variable metal oxide ratios, were obtained. The porous inorganic materials were analyzed in terms of surface area, pore size, film thickness, and crystallinity. The mechanism of nanoparticle infiltration and particle adsorption to the template walls is proposed based on the stability of the inorganic film and a study of the influence of either the sol concentration or washing times on the amount of inorganic substance incorporated in the hybrid material. The photocatalytic decomposition of an organic pollutant, 2-chlorophenol, was demonstrated for the porous titania material along with the structures containing mixtures of titania with zirconia, indium oxide, and tin oxide. A ratio of 9:1 TiO2/MO gave the highest photocatalytic activity, which was higher than the activity of Degussa P25 for the TiO2/In2O3 and TiO2/SnO2 systems under the same conditions. The titania films have also been attached to substrates,glass or indium tin oxide (ITO) surfaces,and the photoelectrochemical properties of the porous film attained. A comparison with a spin-coated titania film (prepared from the same colloidal dispersion) showed that the structured porous inorganic film has two times the photoelectrochemical efficiency as the spin-coated film. [source]

X-ray diffraction of amorphous and crystalline overbased sulphonates

LUBRICATION SCIENCE, Issue 3 2005
Michael T. Costello
Abstract Colloidal dispersions of calcium carbonate stabilised by overbased sulphonates are used as lubricant additives to provide detergency, remove acidity, and prevent wear. In the present work various overbased sulphonate compounds have been analysed using X-ray diffraction (XRD). The amorphous overbased sulphonates studied displayed broad diffraction patterns while the crystalline overbased sulphonates gave well-defined diffraction patterns, correlating with the particle size. The XRD distances of the series of Mg, Ca, and Ba overbased sulphonates shifted to greater values and displayed a clear correlation (r = 0.98) with the ionic radius of the cations used. [source]

Multilayer Amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 Membranes for Hydrogen Purification,,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Ravi Mohan Prasad
Abstract The hydrogen and carbon monoxide separation is an important step in the hydrogen production process. If H2 can be selectively removed from the product side during hydrogen production in membrane reactors, then it would be possible to achieve complete CO conversion in a single-step under high temperature conditions. In the present work, the multilayer amorphous-Si-B-C-N/,-Al2O3/,-Al2O3 membranes with gradient porosity have been realized and assessed with respect to the thermal stability, geometry of pore space and H2/CO permeance. The ,-Al2O3 support has a bimodal pore-size distribution of about 0.64 and 0.045 µm being macroporous and the intermediate ,-Al2O3 layer,deposited from boehmite colloidal dispersion,has an average pore-size of 8,nm being mesoporous. The results obtained by the N2 -adsorption method indicate a decrease in the volume of micropores,0.35 vs. 0.75,cm3,g,1,and a smaller pore size ,6.8 vs. 7.4 Å,in membranes with the intermediate mesoporous ,-Al2O3 layer if compared to those without. The three times Si-B-C-N coated multilayer membranes show higher H2/CO permselectivities of about 10.5 and the H2 permeance of about 1.05,×,10,8 mol m,2 s,1 Pa,1. If compared to the state of the art of microporous membranes, the multilayer Si-B-C-N/,-Al2O3/,-Al2O3 membranes are appeared to be interesting candidates for hydrogen separation because of their tunable nature and high-temperature and high-pressure stability. [source]

Enhanced Optical Properties and Opaline Self-Assembly of PPV Encapsulated in Mesoporous Silica Spheres

ADVANCED FUNCTIONAL MATERIALS, Issue 23 2009
Timothy L. Kelly
Abstract A new poly(p -phenylenevinylene) (PPV) composite material has been developed by the incorporation of insoluble PPV polymer chains in the pores of monodisperse mesoporous silica spheres through an ion-exchange and in situ polymerization method. The polymer distribution within the resultant colloidal particles is characterized by electron microscopy, energy dispersive X-ray microanalysis, powder X-ray diffraction, and nitrogen adsorption. It was found that the polymer was selectively incorporated into the mesopores of the silica host and was well distributed throughout the body of the particles. This confinement of the polymer influences the optical properties of the composite; these were examined by UV,vis and fluorescence spectroscopy and time-correlated single-photon counting. The results show a material that exhibits an extremely high fluorescence quantum yield (approaching 85%), and an improved resistance to oxidative photobleaching compared to PPV. These enhanced optical properties are further complemented by the overall processability of the colloidal material. In marked contrast to the insolubility of PPV, the material can be processed as a stable colloidal dispersion, and the individual composite spheres can be self-assembled into opaline films using the vertical deposition method. The bandgap of the opal can be engineered to overlap with the emission band of the polymer, which has significant ramifications for lasing. [source]

Cover Picture: Composite Silica Spheres with Magnetic and Luminescent Functionalities (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 4 2006
Mater.
Abstract Photographs of a colloidal dispersion of composite nanoparticles with magnetic and luminescent functionalities are shown (left, in column), which are schematically illustrated in the main image. As reported by Salgueiriño-Maceira and co-workers on p.,509, such functionalities are imparted by magnetic and semiconductor nanoparticles within a silica matrix. In the absence of a magnetic field the particles are uniformly dispersed, although they accumulate and can be dragged under the influence of a magnetic field. Their movement can be monitored by their photoluminescence. A new class of highly fluorescent, photostable, and magnetic core/shell nanoparticles in the submicrometer size range has been synthesized from a modified Stöber method combined with the layer-by-layer (LbL) assembly technique. Luminescent magnetic nanoparticles are prepared via two main steps. The first step involves controlled addition of tetraethoxysilane to a dispersion of Fe3O4/,-Fe2O3 nanoparticles, which are thereby homogeneously incorporated as cores into monodisperse silica spheres. The second step involves the LbL assembly of polyelectrolytes and luminescent CdTe quantum dots onto the surfaces of the silica-coated magnetite/maghemite particles, which are finally covered with an outer shell of silica. These spherical particles have a typical diameter of 220,±,10,nm and a saturation magnetization of 1.34,emu,g,1 at room temperature, and exhibit strong excitonic photoluminescence. Nanoparticles with such a core/shell architecture have the added benefit of providing a robust platform (the outer silica shell) for incorporating diverse functionalities into a single nanoparticle. [source]

Inorganic Macroporous Films from Preformed Nanoparticles and Membrane Templates: Synthesis and Investigation of Photocatalytic and Photoelectrochemical Properties,

Drug release properties of polymer coated ion-exchange resin complexes: Experimental and theoretical evaluation

JOURNAL OF PHARMACEUTICAL SCIENCES, Issue 3 2007
Seong Hoon Jeong
Abstract Although ion-exchange resins have been used widely as drug delivery systems, their exact release kinetics has not been reported yet. Usually only the rate-limiting step has been taken into account and the rest of the steps have been ignored as instantaneous processes. To investigate the exact release kinetics of polymer-coated drug/ion-exchange resin complexes for sustained drug delivery, the results of new mathematical modeling were compared with experimental results. Drug/resin complexes with a model drug, dextromethorphan, were prepared and used as cores for fluid-bed coating. An aqueous colloidal dispersion of poly(vinyl acetate) was applied for the coating. A comprehensive mathematical model was developed using a mechanistic approach by considering diffusion, swelling, and ion-exchange processes solved by numerical techniques. The rate-limiting factor of the uncoated resin particles was diffusion through the core matrix. Similarly, in the coated particles the rate-limiting factor was diffusion through the coating membrane. The mathematical model has captured the phenomena observed during experimental evaluations and the release dynamics from uncoated and coated (at different coat levels) particles were predicted accurately (maximum RMSE 2.4%). The mathematical model is a useful tool to theoretically evaluate the drug release properties from coated ion-exchange complexes thus can be used for design purposes. © 2006 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci [source]

One-Pot Synthesis of Functional Helicoidal Hybrid Organic,Inorganic Nanofibers with Periodically Organized Mesoporosity

ADVANCED FUNCTIONAL MATERIALS, Issue 18 2009
Frédéric Rambaud
Abstract The one-pot synthesis and properties of multifunctional hybrid mesoporous organosilica fibers with helical shapes are described. These hybrid mesoporous fibers are prepared without chiral elements and functionalized with a large variety of organic R functions (R,=,alkylthiols, phenylsulfonates, alkylphosphonates, dansyl, aminopropyl, fluoroalkyl, etc.). The resulting nanomaterials are thoroughly characterized by a variety of techniques. The use of a synergetic combination of achiral molecules as co-directing structuring agents, a surfactant, and an organofunctional silica precursor R-Si(OR)3 allows, via carefully tuning of the main synthesis parameters and processing conditions, to control the shape, which is the anisotropic factor, of the hybrid nanofibers. The functionalization of the hybrid materials with fluorescent molecules (dansyl) and gold nanoparticles opens possibilities for sensor and catalytic applications, respectively. Moreover, these hybrid nanofibers can be easily transferred in organic solvents or in a "green" solvent such as water to make stable colloidal dispersions. This tunable functionality of nanofibers also allows their transferability into a variety of polymeric hosts (PVDF, PVBu, and PVP) allowing the formation of functional homogeneous nanocomposite hybrid membranes. [source]

Waterborne, Nanocomposite Pressure-Sensitive Adhesives with High Tack Energy, Optical Transparency, and Electrical Conductivity,

ADVANCED MATERIALS, Issue 20 2006
T. Wang
Transparent and conductive pressure-sensitive adhesives are cast from aqueous colloidal dispersions of poly(butyl acrylate) (P(BuA)) and functionalized carbon nanotubes (CNTs). At the percolation threshold for network formation (at only 0.3,wt,% functionalized CNT), the nanotubes remarkably double the amount of strain at adhesive failure and increase the adhesion energy by 85,% (see figure). The tack properties are explained by current models of adhesive debonding. [source]

Phase and Rheological Behavior of High-Concentration Colloidal Hard-Sphere and Protein Dispersions

JOURNAL OF FOOD SCIENCE, Issue 7 2007
S.M. Loveday
ABSTRACT:, Colloidal hard-sphere (HS) particles of narrow-size distribution exhibit crystalline and glassy states beginning at the particle volume fractions ,= 0.494 and ,G= 0.58, respectively. Dynamic rheological data on the dispersions were strongly modified to solid-like behavior as , approached ,G. In addition, cooperative motion in structural relaxation has been observed microscopically in the colloidal dispersions near the glassy state. Very high viscosities and glassy states were also found in high-concentration dispersions of sodium caseinate and the globular proteins: bovine serum albumin and ,-lactoglobulin. Viscosity models developed for HS dispersions predicted accurately the trends but not the absolute values of protein dispersions. Dispersions of food colloidal particles may be employed in studies, in which volume fraction is the thermodynamic variable, for understanding the relaxation and transport processes related to 1st-order and colloidal glass transitions. [source]

Long-term stability of an ambient self-curable latex based on colloidal dispersions in water of two reactive polymers

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 12 2005
Xiaonong Chen
Abstract An ambient self-curable latex (ASCL) was prepared via the blending of colloidal dispersions in water of a chloromethylstyrene-functionalized copolymer and a tertiary-amine-functionalized copolymer. Upon casting and drying under ambient conditions, the ASCL could generate crosslinked continuous polymer films. The crosslinking occurred via the Menschutkin reaction (quaternization) between the two types of functional groups. Because this reaction was reversible at high temperatures, the films could be decrosslinked and hence were self-curable. The prepared ASCL exhibited excellent colloidal and chemical stability during long-term storage: no significant changes in the colloidal properties, such as the particle size, electrophoretic mobility, and crosslinking reactivity, were observed after 48 months of storage. The electrophoretic measurements indicated that the electrostatic repulsion between the negatively charged particles of the ASCL was responsible for the excellent stability. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2598,2605, 2005 [source]

Synthesis of polybutadiene-based particles via dispersion ring-opening metathesis polymerization

JOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 5 2004
Abraham Chemtob
Abstract Latex particles based on 1,4-polybutadiene were synthesized via dispersion ring-opening metathesis copolymerization of 1,5-cyclooctadiene with a ,-norbornenyl poly(ethylene oxide) macromonomer. Stable but polydisperse colloidal dispersions in the 50 nm to 10 ,m size range were obtained. In this work, particular attention was paid to the effects of the kinetics of copolymerization on the structure of the graft copolymers formed and on the onset of turbidity. Strategies to prepare monodisperse polybutadiene particles were also designed through the growth of a polybutadiene shell from a well-defined polynorbornene seed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1154,1163, 2004 [source]

Surface-enhanced resonance Raman spectroscopy of rifamycins on silver nanoparticles: insight into their adsorption mechanisms

JOURNAL OF RAMAN SPECTROSCOPY, Issue 9 2006
Barry D. Howes
Abstract Three widely used antibiotics from the rifamycin family, rifamycin SV sodium salt, rifampicin and rifaximin, have been characterized by resonance Raman (RR) and surface-enhanced resonance Raman spectroscopy (SERRS). SERRS spectra were recorded using aqueous silver colloidal dispersions prepared with two reducing agents, sodium borohydride and hydroxylamine hydrochloride, for a range of pH values to identify the SERRS-active substrate surface most suitable for each of the three antibiotics. Rifampicin was found to give intense SERRS signals only for the borohydride-reduced colloid and only at pH < 7.7, whereas the hydroxylamine HCl-reduced colloid was the best substrate for rifaximin, giving considerably more intense SERRS spectra than the borohydride colloid. SERRS spectra of rifaximin were observed only at pH < 7.0. It is proposed that the marked pH dependence of the SERRS enhancement results from a transition from an anionic to a neutral zwitterionic state. SERRS spectra of rifamycin SV were not observed for any experimental conditions. The antibiotics display remarkably contrasting SERRS behaviour, reflecting differences in the nature of the substituent groups on the chromophore ring. A vibrational assignment of the RR spectra and detailed comparison between the RR and SERRS data have given insight into the mechanism of adsorption of the antibiotics onto the Ag surface. Rifampicin and rifaximin adsorb adopting an approximately similar vertical orientation of the chromophore ring with respect to the surface; however, rifampicin adsorbs by direct chemical interaction with the Ag whereas rifaximin does not form a direct bond with the Ag surface. Copyright © 2006 John Wiley & Sons, Ltd. [source]