Colloidal Suspensions (colloidal + suspension)

Distribution by Scientific Domains


Selected Abstracts


Filtration of Colloidal Suspensions , MRI Investigation and Numerical Simulation

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 7 2006
A. Erk
Abstract The principle mechanisms of solid-liquid separation processes are sedimentation and filtration, both including the formation and compression of a liquid-saturated bulk. The compressive properties of the bulk determine the operating parameters of solid-liquid separation devices and the achievable separation results. Information about the solids volume fraction of the bulk is essential for a better understanding of the physical mechanisms and precise modeling. A numerical model for the calculation of the local solids volume fraction during formation and compression of filter cakes and sediments was developed. The calculated results are compared with experimental NMR data. [source]


An autonomous phase-boundary detection technique for colloidal hard sphere suspension experiments,

MICROSCOPY RESEARCH AND TECHNIQUE, Issue 4 2006
Mark McDowell
Abstract Colloidal suspensions of monodisperse spheres are used as physical models of thermodynamic phase transitions and as precursors to photonic band gap materials. Current techniques for identifying the phase boundaries involve manually identifying the phase transitions, which is very tedious and time-consuming. In addition, current image analysis techniques are not able to distinguish between densely packed phases within conventional microscope images, which are mainly characterized by degrees of randomness or order with similar grayscale value properties. We have developed an intelligent machine vision technique that automatically identifies colloidal phase boundaries. The technique utilizes intelligent image processing algorithms that accurately identify and track phase changes vertically or horizontally for a sequence of colloidal hard sphere suspension images. This technique is readily adaptable to any imaging application wherein regions of interest are distinguished from the background by differing patterns of motion over time. Microsc. Res. Tech. 69:236,245, 2006. Published 2006 Wiley-Liss, Inc. [source]


The effect of contact load reduction on the fatigue life of pearlitic rail steel in lubricated rolling,sliding contact

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2000
D. I. Fletcher
Twin-disc contact simulation tests were carried out to investigate the influence of contact pressure variation on rail steel fatigue life. Both a colloidal suspension of molybdenum disulphide in an oil carrier fluid (similar to a commercial flange lubrication product) and water were used as lubricants. It was found that the reduction from 1500 to 900 MPa of the maximum Hertzian contact pressure (at which a molybdenum,disulphide-lubricated and previously worn rail sample was tested) extended the fatigue life of the rail steel by over five times. For water lubrication a similar reduction in contact pressure produced only a marginal increase in fatigue life. The results were found to be in qualitative agreement with the predictions of the newly developed Three Mechanism (TM) model of rolling contact fatigue, which is introduced here. This model combines the mechanisms of ratcheting and the fracture mechanics-based mechanisms of both shear stress- and tensile stress-driven, fluid-assisted, crack growth. [source]


A Controllable Self-Assembly Method for Large-Scale Synthesis of Graphene Sponges and Free-Standing Graphene Films

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Fei Liu
Abstract A simple method to prepare large-scale graphene sponges and free-standing graphene films using a speed vacuum concentrator is presented. During the centrifugal evaporation process, the graphene oxide (GO) sheets in the aqueous suspension are assembled to generate network-linked GO sponges or a series of multilayer GO films, depending on the temperature of a centrifugal vacuum chamber. While sponge-like bulk GO materials (GO sponges) are produced at 40,C, uniform free-standing GO films of size up to 9,cm2 are generated at 80,C. The thickness of GO films can be controlled from 200,nm to 1,m based on the concentration of the GO colloidal suspension and evaporation temperature. The synthesized GO films exhibit excellent transparency, typical fluorescent emission signal, and high flexibility with a smooth surface and condensed density. Reduced GO sponges and films with less than 5,wt% oxygen are produced through a thermal annealing process at 800,C with H2/Ar flow. The structural flexibility of the reduced GO sponges, which have a highly porous, interconnected, 3D network, as well as excellent electrochemical properties of the reduced GO film with respect to electrode kinetics for the [Fe(CN)6]3,/4, redox system, are demonstrated. [source]


Electric Field-Directed Convective Assembly of Ellipsoidal Colloidal Particles to Create Optically and Mechanically Anisotropic Thin Films

ADVANCED FUNCTIONAL MATERIALS, Issue 20 2009
Manish Mittal
Abstract A method of simultaneous field- and flow-directed assembly of anisotropic titania (TiO2) nanoparticle films from a colloidal suspension is presented. Titania particles are oriented by an alternating (ac) electric field as they simultaneously advect towards a drying front due to evaporation of the solvent. At high field frequencies (,,>,,25,kHz) and field strengths (E,>,300,V cm,1), the particles orient with their major axis along the field direction. As the front recedes, a uniform film with thicknesses of 1,10,m is deposited on the substrate. The films exhibit a large birefringence (,n,,,0.15) and high packing fraction (,,=,0.75,,0.08), due to the orientation of the particles. When the frequency is lowered, the particle orientation undergoes a parallel,random,perpendicular transition with respect to the field direction. The orientation dependence on field frequency and strength is explained by the polarizability of ellipsoidal particles using an interfacial polarization model. Particle orientation in the films also leads to anisotropic mechanical properties, which are manifested in their cracking patterns. In all, it is demonstrated that the field-directed assembly of anisotropic particles provides a powerful means for tailoring nanoparticle film properties in situ during the deposition process. [source]


Fabrication of Ordered Nanostructured Arrays Using Poly(dimethylsiloxane) Replica Molds Based on Three-Dimensional Colloidal Crystals

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2009
Hong Kyoon Choi
Abstract Hexagonally arrayed structures of colloidal crystals with uniform surface are a good candidate for master molds to be used in soft lithography. Here, the fabrication of periodically arrayed nanostructures using poly(dimethylsiloxane) (PDMS) molds based on three-dimensionally (3D) ordered colloidal crystals is reported. A robust, high-quality 3D colloidal-crystal master molds is prepared using the colloidal suspension containing a water-soluble polymer. The surface patterns of the 3D colloidal crystals can then be transferred onto a polymer film via soft lithography, by means of the replication of the surface pattern with PDMS. Various hexagonally arrayed nanostructure patterns can be fabricated, including close-packed and non-close-packed 2D arrays and honeycomb structures by the structural modification of the 3D colloidal-crystal templates. The replicated hexagonally arrayed structures can also be used as templates for producing colloidal crystals with 2D superlattices. [source]


Electrospray-Assisted Fabrication of Uniform Photonic Balls,

ADVANCED MATERIALS, Issue 7 2004
H. Moon
Photonic balls have been fabricated (see Figure) by field-enhanced electrospray of an aqueous colloidal suspension. The polystyrene (PS) beads inside the suspension droplets self-organize into opaline balls while the solvent evaporates. The opaline balls are used as templates for inverse opaline photonic balls, and both types exhibit varying reflection colors depending on the diameter of the beads and the reflective index contrast. [source]


1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)- pentane-2,4-dione,synthesis, spectroscopic, theoretical and structural elucidation

JOURNAL OF PHYSICAL ORGANIC CHEMISTRY, Issue 12 2007
Tsonko M. Kolev
Abstract 1,1,1-Trichloro-3-(1-phenethylamino-ethylidene)-pentane-2,4-dione is spectroscopically and structurally elucidated by means of linear-polarized IR spectroscopy (IR-LD) of oriented solids as a colloidal suspension in nematic liquid crystal. Structural information and IR-spectroscopic assignment are supported by quantum chemical calculations at MP2 and B3LYP level of theory and 6-311++G** basis set. The geometry is characterized with an inramolecular hydrogen bond of NH,OC with length of 2.526, and a NHO angle of 140.5(1). The NHC(CH3)CCCO(CH3) fragment is nearly flat with a maximal deviation of total planarity of 10.4. Copyright 2007 John Wiley & Sons, Ltd. [source]


Synthesis, Surface Modifications, and Size-Sorting of Mixed Nickel,Zinc Ferrite Colloidal Magnetic Nanoparticles

CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2008
P. Majewski
Abstract We report on the spontaneous covalent growth of monomolecular adlayers on mixed nickel,zinc nanoferrite colloidal suspensions (ferrofluids). Synthesized nanoparticles were subjected to surface modification by means of acid chloride chemistry, leading to the formation of covalent bonds between the hydroxy groups at the nanoparticle surface and the acid chloride molecules. This procedure can be easily tailored to allow for the formation of adlayers containing both hydrophobic and hydrophilic regions stacked at predetermined distances from the magnetic core, and also providing the nanoferrites with functional carboxy groups capable of further modifications with, for example, drug molecules. Here, fluorophore aminopyrene molecules were bound to such modified nanoferrites through amide bonds. We also used the same chemistry to modify the surface with covalently bound long-chain palmitoyl moieties, and for comparison we also modified the nanoferrite surface by simple adsorption of oleic acid. Both procedures made the surface highly hydrophobic. These hydrophobic colloids were subsequently spread on an aqueous surface to form Langmuir monolayers with different characteristics. Moreover, since uniformity of size is crucial in a number of applications, we propose an efficient way of sorting the magnetic nanoparticles by size in their colloidal suspension. The suspension is centrifuged at increasing rotational speed and the fractions are collected after each run. The mean size of nanoferrite in each fraction was measured by the powder X-ray diffraction (PXRD) technique. [source]


Stable Inverted Polymer/Fullerene Solar Cells Using a Cationic Polythiophene Modified PEDOT:PSS Cathodic Interface

ADVANCED FUNCTIONAL MATERIALS, Issue 15 2010
David A. Rider
Abstract A cationic and water-soluble polythiophene [poly[3-(6-pyridiniumylhexyl)thiophene bromide] (P3PHT+Br,)] is synthesized and used in combination with anionic poly(3,4-ethylenedioxythiophene):poly(p -styrenesulfonate) (PEDOT:PSS), to produce hybrid coatings on indium tin oxide (ITO). Two coating strategies are established: i) electrostatic layer-by-layer assembly with colloidal suspensions of (PEDOT:PSS),, and ii) modification of an electrochemically prepared (PEDOT:PSS), film on ITO. The coatings are found to modify the work function of ITO such that it could act as a cathode in inverted 2,5-diyl-poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl-C61 -butyric acid methyl ester (PCBM) polymer photovoltaic cells. The interfacial modifier created from the layer-by-layer assembly route is used to produce efficient inverted organic photovoltaic devices (power conversion efficiency ,2%) with significant long-term stability in excess of 500,h. [source]


Simultaneous light and small-angle neutron scattering on aggregating concentrated colloidal suspensions

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 1 2003
Sara Romer
A new sample environment has been developed in order to perform light and small-angle neutron scattering (SANS) simultaneously on colloidal systems. The combination of SANS and diffusing wave spectroscopy (DWS) is of particular use in the high-concentration regime. DWS provides information on the local dynamic properties of the individual particles, whereas SANS gives access to the structural properties on similar length scales. The combination of both methods thus allows one to obtain structural and dynamic information over a very large range of length and time scales. Using this new setup, the onset of aggregation and the sol,gel transition in concentrated destabilized polystyrene sphere suspensions have been investigated. At the gel point, a dramatic change of the particle dynamics from diffusion to a subdiffusive arrested motion is observed. However, while the DWS measurements indicate that dramatic changes in the local dynamics occur over a long period, the SANS pattern quickly reaches its final appearance. The SANS experiments thus indicate that a fluid-like structure is arrested in the course of the gel formation. The data are found to be in good qualitative agreement with computer simulations. [source]


Estimation of the hindered settling function R(,) from batch-settling tests

AICHE JOURNAL, Issue 4 2005
Daniel R. Lester
Abstract The hindered settling function R(,) is a material function that quantifies the interphase drag of colloidal suspensions for all solids volume fractions ,. A method is presented to estimate R(,) from batch-settling tests for solids volume fractions between the initial solids volume fraction, ,0, and the solids volume fraction at which the suspension forms a continuously networked structure, ,g, known as the gel point. The method is based on an analytic solution of the associated inverse problem. Techniques are presented to address initialization mechanics observed in such tests as well as experimental noise and discrete data. Analysis of synthetic and experimental data suggests that accurate estimates of R(,) are possible in most cases. These results provide scope for characterization of suspension dewaterability from batch-settling tests alone. 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]


Reaction-limited aggregation in presence of short-range structural forces

AICHE JOURNAL, Issue 4 2005
Venkataramana Runkana
Abstract A geometrically discretized sectional population balance model for reaction-limited aggregation of colloidal suspensions is presented. The two important model parameters are collision frequency factor and collision efficiency factor. The collision frequency factor is derived from physically realistic arguments proposed for collision of fractal aggregates. The collision efficiency factor is computed as a function of total interaction energy between particles, including short-range structural repulsion forces. The irregular and open structure of aggregates is taken into account by incorporating their mass fractal dimension. The characteristic time constant of reaction-limited aggregation, derived from dynamic scaling of mean aggregate size-aggregation time data, is found to correlate with electrolyte concentration. The population balance model is tested with published experimental data for aggregation of ,-alumina suspensions in the presence of different electrolytes. It is shown that the slow kinetics of aggregation under certain conditions of pH and electrolyte concentration require inclusion of short-range structural repulsion forces along with van der Waals attraction and electrical double layer repulsion forces in an extended DLVO theory. The model predictions are in good agreement with experimental data for time evolution of mean aggregate diameter in the reaction-limited aggregation regime. 2005 American Institute of Chemical Engineers AIChE J, 2005 [source]


In Situ X-Ray Radiography and Tomography Observations of the Solidification of Aqueous Alumina Particle Suspensions,Part I: Initial Instants

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 11 2009
Sylvain Deville
This paper investigates by in situ high-resolution X-ray radiography and tomography the behavior of colloidal suspensions of alumina partic les during directional solidification by freezing. The combination of these techniques provided both qualitative and quantitative information about the propagation kinetic of the solid/liquid interface, the particle redistribution between the crystals and a particle-enriched phase, and the three-dimensional organization of the ice crystals. In this first part of two companion papers, the precursor phenomena leading to directional crystallization during the first instants of solidification are studied. Mullins,Sekerka instabilities are not necessary to explain the dynamic evolution of the interface pattern. Particle redistribution during these first instants is dependent on the type of crystals growing into the suspension. The insights gained into the mechanisms of solidification of colloidal suspensions may be valuable for the materials processing routes derived for this type of directional solidification (freeze-casting), and of general interest for those interested in the interactions between solidification fronts and inert particles. [source]


Phase Behavior, 3-D Structure, and Rheology of Colloidal Microsphere,Nanoparticle Suspensions

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2006
Summer K. Rhodes
A new route for tailoring the behavior of colloidal suspensions through nanoparticle additions is reviewed. Specifically, the interparticle interactions, phase behavior, 3-D structure, and rheological properties of microsphere,nanoparticle mixtures that possess both high charge and size asymmetry are described. Negligibly charged microspheres, which flocculate when suspended alone, undergo a remarkable stabilizing transition upon the addition of highly charged nanoparticles. The formation of a dynamic nanoparticle halo around each colloid induces an effective repulsion between the microspheres that promotes their stability. With increasing nanoparticle concentration, the colloids again undergo flocculation because of the emergence of an effective microsphere attraction, whose magnitude exhibits a quadratic dependence on nanoparticle volume fraction. The broader impact of these observations on colloidal stabilization and assembly of advanced ceramics is highlighted. [source]


Effect of Ultrasonication on the Microstructure and Tensile Elongation of Zirconia-Dispersed Alumina Ceramics Prepared by Colloidal Processing

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2001
Tohru S. Suzuki
To obtain dense, fine-grained ceramics, fine particles and advanced powder processing, such as colloidal processing, are needed. Al2O3 and ZrO2 particles are dispersed in colloidal suspensions by electrosteric repulsion because of polyelectrolyte absorbed on their surfaces. However, additional redispersion treatment such as ultrasonication is required to obtain dispersed suspensions because fine particles tend to agglomerate. The results demonstrate that ultrasonication is effective in improving particle dispersion in suspensions and producing a homogeneous fine microstructure of sintered materials. Superplastic tensile ductility is improved by ultrasonication in preparing suspensions because of the dense and homogeneous fine microstructure. [source]


Correlations and Fluctuations of Charged Colloids as Determined by Anomalous Small-Angle X-Ray Scattering

MACROMOLECULAR THEORY AND SIMULATIONS, Issue 3 2006
Arben Jusufi
Abstract Summary: We performed molecular dynamics simulation of a charged colloidal particle with explicit counterions. Our work provides a direct comparison between simulations and ASAXS-experiments, offering insight into the counterion distribution of charged colloidal suspensions. We give a detailed constitution of the appearing scattering terms with their physical meaning. It is shown that the cross-correlation between a macroion and its counterions gives the meanfield approximation of the counterion density even if the counterion system is highly fluctuating. Furthermore, it is shown that cross-correlations can be negative due to oscillations of the density amplitudes of the macroion and counterions and, therefore, must be distinguished from other scattering contributions. These oscillations become more pronounced if the counterions exhibit a fixed shape and if the size of the macroion and that of the counterion system are different. Simulation sanpshot of a charged colloid (big central sphere) with counterions (small spheres). [source]


Electrochemical synthesis and stabilization of cobalt nanoparticles

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 6 2006
A. Ledo-Surez
Abstract Cobalt nanoparticles (NPs) were synthesized via an electrochemical method in the presence of tetraalkylammonium salt. The nanometer dimensions of the NPs can be controlled in a simple way by adjustment of the current density. From these particles stable colloidal suspensions are prepared in the presence of a fatty acid (oleic acid) and triphenylphosphine. The colloidal system is stable against oxidation when they are kept in heptane (C7H16). Transmission electron microscopy (TEM) was employed to determine the core size and the shape of metal nanoparticles. The chemical interaction of the surfactant with the Co nanoparticles was studied by using Fourier transform infrared spectroscopy (FTIR) and nuclear magnetic resonance (NMR). Thermogravimetric analysis (TGA) was used to study the thermal stability and the composition of the capped cobalt nanoparticles. ( 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]


Production of Highly Loaded Nanocomposites by Dispersing Nanoparticles in Epoxy Resin

CHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 9 2010
H. Nolte
Abstract The objective of this study was the investigation of techniques for dispersing alumina nanoparticles with different surface modifications in epoxy resin. In order to prepare the matrix suspension, high contents of fillers (up to 50,wt,%) were dispersed by conducting shear mixing techniques in a high performance laboratory kneader. The intention was to attain solutions that were stable against re-agglomeration, while the mass fraction and the product fineness were maintained as high as possible. Therefore, both the formulations and the dispersion parameters were varied systematically. An epoxy resin was used as a carrier fluid and a corresponding amine hardener system was chosen. Tests were performed using alumina particles and surface modified alumina particles at different particle concentrations. Furthermore, the effect of diluting the colloidal suspensions and the resulting long term stability were also examined. The matrix suspension was examined with respect to viscosity, stability and particle size distribution. [source]


Synthesis, Surface Modifications, and Size-Sorting of Mixed Nickel,Zinc Ferrite Colloidal Magnetic Nanoparticles

CHEMISTRY - A EUROPEAN JOURNAL, Issue 26 2008
P. Majewski
Abstract We report on the spontaneous covalent growth of monomolecular adlayers on mixed nickel,zinc nanoferrite colloidal suspensions (ferrofluids). Synthesized nanoparticles were subjected to surface modification by means of acid chloride chemistry, leading to the formation of covalent bonds between the hydroxy groups at the nanoparticle surface and the acid chloride molecules. This procedure can be easily tailored to allow for the formation of adlayers containing both hydrophobic and hydrophilic regions stacked at predetermined distances from the magnetic core, and also providing the nanoferrites with functional carboxy groups capable of further modifications with, for example, drug molecules. Here, fluorophore aminopyrene molecules were bound to such modified nanoferrites through amide bonds. We also used the same chemistry to modify the surface with covalently bound long-chain palmitoyl moieties, and for comparison we also modified the nanoferrite surface by simple adsorption of oleic acid. Both procedures made the surface highly hydrophobic. These hydrophobic colloids were subsequently spread on an aqueous surface to form Langmuir monolayers with different characteristics. Moreover, since uniformity of size is crucial in a number of applications, we propose an efficient way of sorting the magnetic nanoparticles by size in their colloidal suspension. The suspension is centrifuged at increasing rotational speed and the fractions are collected after each run. The mean size of nanoferrite in each fraction was measured by the powder X-ray diffraction (PXRD) technique. [source]


Stereo- and Biochemical Profiles of the 5-6- and 6-6-Junction Isomers of , - D -Mannopyranosyl [60]Fullerenes

CHEMISTRY & BIODIVERSITY, Issue 10 2004
Yoshihiro Nishida
The 5-6- and 6-6-junction isomers of , - D -mannopyranosyl [60]fullerene were studied by means of circular dichroism (CD), deuterium labeling, 1H-NMR, molecular-dynamics (MD) calculations, and a lectin-binding assay. The CD spectra of the O -acetylated derivatives allowed clear discrimination of the isomers, while the 1H-NMR spectra, with assistance from deuterium labeling and MD calculations, served to disclose the unique conformation and molecular geometry of each acetylated isomer in chloroform solution. The deprotected 5-6- and 6-6-isomers, which gave colloidal suspensions in aqueous mixtures, displayed marked activity in blocking lectin-induced hemagglutination by concanavalin,A. [source]