Showing papers on "Particle published in 2002"
TL;DR: In this paper, the authors compare the behavior observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.
Abstract: Colloidal particles act in many ways like surfactant molecules, particularly if adsorbed to a fluid–fluid interface. Just as the water or oil-liking tendency of a surfactant is quantified in terms of the hydrophile–lipophile balance (HLB) number, so can that of a spherical particle be described in terms of its wettability via contact angle. Important differences exist, however, between the two types of surface-active material, due in part to the fact that particles are strongly held at interfaces. This review attempts to correlate the behaviour observed in systems containing either particles or surfactant molecules in the areas of adsorption to interfaces, partitioning between phases and solid-stabilised emulsions and foams.
3,202 citations
TL;DR: In this paper, the authors explore four possible explanations for the anomalous thermal conductivity of nanofluids: Brownian motion of the particles, molecular-level layering of the liquid at the liquid/particle interface, the nature of heat transport in the nanoparticles, and the effects of nanoparticle clustering.
2,008 citations
TL;DR: In this paper, the effect of size and shape on the spectral response of individual silver nanoparticles was studied and it was shown that specific geometrical shapes give distinct spectral responses.
Abstract: We present a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. An experimental method has been developed that begins with the detection and characterization of isolated nanoparticles in the optical far field. The plasmon resonance optical spectrum of many individual nanoparticles are then correlated to their size and shape using high-resolution transmission electron microscopy. We find that specific geometrical shapes give distinct spectral responses. In addition, inducing subtle changes in the particles’ morphology by heating causes a shift in the individual particle spectrum and provides a simple means of tuning the spectral response to a desired optical wavelength. Improved colloidal preparation methods could potentially lead to homogeneous populations of identical particle shapes and colors. These multicolor colloids could be used as biological labels, surface enhanced Raman scattering substrates, or near field optical microscopy sources cove...
1,687 citations
TL;DR: A new numerical method for improving the mass conservation properties of the level set method when the interface is passively advected in a flow field that compares favorably with volume of fluid methods in the conservation of mass and purely Lagrangian schemes for interface resolution.
1,120 citations
TL;DR: In this article, a review of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids is presented, where the stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed.
Abstract: Some of the most relevant finite-size and surface effects in the magnetic and transport properties of magnetic fine particles and granular solids are reviewed. The stability of the particle magnetization, superparamagnetic regime and the magnetic relaxation are discussed. New phenomena appearing due to interparticle interactions, such as the collective state and non-equilibrium dynamics, are presented. Surface anisotropy and disorder, spin-wave excitations, as well as the enhancements of the coercive field and particle magnetization are also reviewed. The competition of surface and finite-size effects to settle the magnetic behaviour is addressed. Finally, two of the most relevant phenomena in the transport properties of granular solids are summarized namely, giant magnetoresistance in granular heterogeneous alloys and Coulomb gap in insulating granular solids.
1,083 citations
TL;DR: The catalytic performance of Au nanoparticles is defined by three major factors: contact structure, support selection, and particle size, the first being the most important because the perimeter interfaces around Au particles act as the site for reaction as discussed by the authors.
Abstract: Gold in bulk is chemically inert and has often been regarded to be poorly active as a catalyst. However, when gold is small enough—with particle diameters below 10 nm—it turns out to be surprisingly active for many reactions, such as CO oxidation and propylene epoxidation. This is especially so at low temperatures. Here, a summary of the catalysis of Au nanoparticles deposited on base metal oxides is presented. The catalytic performance of Au is defined by three major factors: contact structure, support selection, and particle size, the first of which being the most important because the perimeter interfaces around Au particles act as the site for reaction.
1,042 citations
TL;DR: In this article, a transient hot-wire method was used to investigate the thermal conductivity of Al2O3 nanoparticles with specific surface areas in a range of 5 −124 m2 g−1.
Abstract: Various suspensions containing Al2O3 nanoparticles with specific surface areas in a range of 5–124 m2 g−1 have been prepared and their thermal conductivities have been investigated using a transient hot-wire method. Nanoparticle suspensions, containing a small amount of Al2O3, have substantially higher thermal conductivity than the base fluid, with the enhancement increasing with the volume fraction of Al2O3. The enhanced thermal conductivity increases with an increase in the difference between the pH value of aqueous suspension and the isoelectric point of Al2O3 particle. For the suspensions using the same base fluid, the thermal conductivity enhancements are highly dependent on specific surface area (SSA) of nanoparticle, with an optimal SSA for the highest thermal conductivity. For the suspensions containing the same nanoparticles, the enhanced thermal conductivity ratio is reduced with the increasing thermal conductivity of the base fluid. The crystalline phase of the nanoparticles appears to have no ...
939 citations
TL;DR: In this article, the electrical and thermal conductivity of systems based on epoxy resin (ER) and polyvinyl chloride (PVC) filled with metal powders have been studied.
933 citations
TL;DR: Bessel beams do not diverge and, furthermore, if part of the beam is obstructed or distorted the beam reconstructs itself after a characteristic propagation distance, which may be utilized within optical tweezers to trap particles in multiple, spatially separated sample cells with a single beam.
Abstract: Optical tweezers1 are commonly used for manipulating microscopic particles, with applications in cell manipulation2, colloid research3,4,5, manipulation of micromachines6 and studies of the properties of light beams7. Such tweezers work by the transfer of momentum from a tightly focused laser to the particle, which refracts and scatters the light and distorts the profile of the beam. The forces produced by this process cause the particle to be trapped near the beam focus. Conventional tweezers use gaussian light beams, which cannot trap particles in multiple locations more than a few micrometres apart in the axial direction, because of beam distortion by the particle and subsequent strong divergence from the focal plane. Bessel beams8,9, however, do not diverge and, furthermore, if part of the beam is obstructed or distorted the beam reconstructs itself after a characteristic propagation distance10. Here we show how this reconstructive property may be utilized within optical tweezers to trap particles in multiple, spatially separated sample cells with a single beam. Owing to the diffractionless nature of the Bessel beam, secondary trapped particles can reside in a second sample cell far removed (∼3 mm) from the first cell. Such tweezers could be used for the simultaneous study of identically prepared ensembles of colloids and biological matter, and potentially offer enhanced control of ‘lab-on-a-chip’ and optically driven microstructures.
914 citations
TL;DR: The application of dielectrophoresis to particle discrimination, separation, and fractionation is reviewed, some advantages and disadvantages of currently available approaches are considered, and some caveats are noted.
Abstract: The application of dielectrophoresis to particle discrimination, separation, and fractionation is reviewed, some advantages and disadvantages of currently available approaches are considered, and some caveats are noted.
811 citations
TL;DR: In this paper, the effect of oxidant and precursor fuel composition on the size of FSP-made silica primary particles (8 − 40 nm ) was studied using as precursor hexamethyldisiloxane (HMDSO) dissolved in ethanol, iso-octane or methanol.
TL;DR: In this article, supercritical carbon dioxide, an environmentally friendly, low-cost, non-flammable, chemically benign gas is used as the blowing agent to create microcellular foam.
TL;DR: In this article, a review of recent developments in the electrodeposition of ceramics and organoceramic materials is presented, which includes mass transport, accumulation of particles near the electrode and their coagulation to form a cathodic deposit, and interparticle forces that govern colloidal stability in the absence and presence of processing additives.
TL;DR: In this paper, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold spray process, and the modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity that is specific to the spray material.
Abstract: In this study, computational fluid dynamics (CFD) and extensive spray tests were performed for detailed analyses of the cold spray process. The modeling of the gas and particle flow field for different nozzle geometries and process parameters in correlation with the results of the experiments reveal that adhesion only occurs when the powder particles exceed a critical impact velocity that is specific to the spray material. For spherical copper powder with low oxygen content, the critical velocity was determined to be about 570 m/s. With nitrogen as the process gas and particle grain sizes from 5–25 µm, deposition efficiencies of more than 70% were achieved. The cold sprayed coatings show negligible porosity and oxygen contents comparable to the initial powder feedstock. Therefore, properties such as the electrical conductivity at room temperature correspond to those of the bulk material. The methods presented here can also be applied to develop strategies for cold spraying of other materials such as zinc, stainless steel, or nickel-based super-alloys.
TL;DR: In this paper, a finite element analysis, employing a specialised computational fluid dynamics package, is used to simulate the fluid flow, and thus dispersion of reinforcement material in a molten matrix alloy during stirring.
TL;DR: In this paper, a model was developed based on the mechanistic steps in photocatalysis to elucidate the role of particle size on the apparent photoactivity of TiO2 for the photooxidation of organic substrates in water.
TL;DR: This paper introduces the method of live-cell multiple-particle-tracking microrheology (MPTM), which quantifies the local mechanical properties of living cells by monitoring the Brownian motion of individual microinjected fluorescent particles, and investigates the mechanical function of alpha-actinin in non-muscle cells.
TL;DR: It is proposed that defects, such as vacancies, at the bimetallic interface enhance the radial migration (as well as displacement around the interface) of one metal into the other at the room temperature interdiffusion.
Abstract: We report on systematic studies of size-dependent alloy formation of silver-coated gold nanoparticles (NPs) in aqueous solution at ambient temperature using X-ray absorption fine structure spectroscopy (XAFS). Various Au-core sizes (2.5−20 nm diameter) and Ag shell thicknesses were synthesized using radiolytic wet techniques. The equilibrium structures (alloy versus core−shell) of these NPs were determined in the suspensions. We observed remarkable size dependence in the room temperature interdiffusion of the two metals. The interdiffusion is limited to the subinterface layers of the bimetallic NPs and depends on both the core size and the total particle size. For the very small particles (≤4.6 nm initial Au-core size), the two metals are nearly randomly distributed within the particle. However, even for these small Au-core NPs, the interdiffusion occurs primarily in the vicinity of the original interface. Features from the Ag shells do remain. For the larger particles, the boundary is maintained to withi...
TL;DR: The cage sizes and lifetimes are measured, which, respectively, shrink and grow as the glass transition approaches, and are found to be more prevalent in regions with lower concentrations and higher disorder.
Abstract: We use confocal microscopy to study particle motion in colloidal systems. Near the glass transition, motion is inhibited, as particles spend time trapped in transient "cages" formed by neighboring particles. We measure the cage sizes and lifetimes, which, respectively, shrink and grow as the glass transition approaches. Cage rearrangements are more prevalent in regions with lower concentrations and higher disorder. Neighboring rearranging particles typically move in parallel directions, although a nontrivial fraction moves in antiparallel directions, usually from particle pairs with initial separations corresponding to local maxima and minima of the pair correlation function g(r), respectively.
TL;DR: The behavior of heavy particles in isotropic, homogeneous, decaying turbulence has been experimentally studied and the settling velocity of the particles has been found to be much larger than in a quiescent fluid as mentioned in this paper.
Abstract: The behaviour of heavy particles in isotropic, homogeneous, decaying turbulence has been experimentally studied The settling velocity of the particles has been found to be much larger than in a quiescent fluid It has been determined that the enhancement of the settling velocity depends on the particle loading, increasing as the volume fraction of particles in the flow increases The spatial and temporal distribution of the particle concentration field is shown to exhibit large inhomogeneities As the particles interact with the underlying turbulence they concentrate preferentially in certain regions of the flow A characteristic dimension of these particle clusters is found to be related to the viscous scales of the flow Measurements of the settling velocity conditioned on the local concentration of particles in the flow have shown that there is a monotonic increase in the settling velocity with the local concentration (the relation being quasi-linear) A simple phenomenological model is proposed to explain this behaviour
TL;DR: In this paper, the authors presented a numerical and experimental study of the angle of repose of mono-sized coarse spheres, a most important macroscopic parameter in characterising granular materials.
TL;DR: In this paper, a simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions.
Abstract: A simple one-step procedure is described for the synthesis of spherical mesoporous silica, in which the size of the particles is controlled over a range of diameters from 65 to 740 nm by varying the initial silicate/surfactant concentration under dilute conditions. The particles were characterized using X-ray diffraction, transmission electron microscopy, and liquid nitrogen adsorption. Synthesis using a charged template, cetyltrimethylammonium bromide, under aqueous conditions yielded particles of irregular spherical shape with highly ordered mesoporous channels. Synthesis under ethanol/water cosolvent conditions yielded smooth spheres with a starburst mesopore structure extending from the center of the particle to the circumference. All materials were thermally stable and exhibited two steps in their liquid nitrogen isotherms corresponding to reversible channel filling and non-reversible adsorption between particles. Mesopore volumes varied from 0.64 to 0.93 cm3 g-1 and surface areas varied from 917 to ...
TL;DR: In this paper, the effects of furnishings and air speed on particle deposition to surfaces have been investigated in an isolated room (volume=14.2m3) using three different indoor furnishing levels (bare, carpeted, and fully furnished) and four different air flow conditions.
TL;DR: In this article, a three-phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (E-c).
Abstract: Based on Takayanagi's two-phase model, a three-phase model including the matrix, interfacial region, and fillers is proposed to calculate the tensile modulus of polymer nanocomposites (E-c). In this model, fillers (sphere-, cylinder- or plate-shape) are randomly distributed in a matrix. If the particulate size is in the range of nanometers, the interfacial region will play an important role in the modulus of the composites. Important system parameters include the dispersed particle size (t), shape, thickness of the interfacial region (tau), particulate-to-matrix modulus ratio (E-d/E-m), and a parameter (k) describing a linear gradient change in modulus between the matrix and the surface of particle on the modulus of nanocomposites (E-c). The effects of these parameters are discussed using theoretical calculation and nylon 6/montmorillonite nanocomposite experiments. The former three factors exhibit dominant influence on E-c At a fixed volume fraction of the dispersed phase, smaller particles provide an increasing modulus for the resulting composite, as compared to the larger one because the interfacial region greatly affects E-c. Moreover, since the size of fillers is in the scale of micrometers, the influence of interfacial region is neglected and the deduced equation is reduced to Takayanagi's model. The curves predicted by the three-phase model are in good agreement with experimental results. The percolation concept and theory are also applied to analyze and interpret the experimental results.
TL;DR: In this article, the rate of energy dissipation from Au nanoparticles to their surroundings has been examined by pump-probe spectroscopy, and the results show that energy relaxation is a very nonexponential process.
Abstract: The rate of energy dissipation from Au nanoparticles to their surroundings has been examined by pump−probe spectroscopy. These experiments were performed for particles suspended in aqueous solution, with average sizes ranging from 4 to 50 nm in diameter. The results show that energy relaxation is a very nonexponential process. Fitting the data to a stretched exponential function yields a characteristic time scale for relaxation that varies from ca. 10 ps for the smallest particles examined (∼4 nm diameter) to almost 400 ps for the 50 nm diameter particles. The relaxation times are proportional to the square of the radius, but do not depend on the initial temperature of the particles (i.e., the pump laser power). For very small particles, the time scale for energy dissipation is comparable to the time scale for electron−phonon coupling, which implies that significant energy loss occurs before the electrons and phonons reach thermal equilibrium within the particle.
TL;DR: In this article, a comprehensive model for kinetic spray coating formation is proposed based on observations reported in this paper, and four velocity-dependent stages of coating formation are proposed based upon observations reported here, which are consistent with a metallic form for tensile tests on Al coatings removed from the substrate.
Abstract: Coatings have been produced by entraining relatively large diameter metal powders in a supersonic airflow. For the first time, most of the particles in the powders have diameters >50 μm. Substantial plastic deformation is involved in the conversion of the particle's kinetic energy into heat and strain energy in this kinetic spray process. As suggested by simple estimates and confirmed by coating grain structures, the particles are not melted or thermally softened in this coating process. These coatings have a relatively low oxide content, low thermal stress, high adhesion, low porosity and hardness somewhat higher than those of corresponding bulk materials. Threshold or critical velocities for coating formation are discussed. Critical velocities for the relatively large particles were observed to be substantially less than have been reported earlier for smaller diameter (<50 μm) particles. Coating particle rotation and deformation due to particle impact resulted in a corresponding decrease in porosity. Bond formation, particle deformation and grain deformation were found to be highly anisotropic, depending on the direction of the incident particle velocity. At higher incident velocities, increasing metallic bond formation between particles was observed. This is consistent with a metallic form for stress/strain curves obtained via tensile tests on Al coatings removed from the substrate. The coating elastic modulus was found to be less than half that of bulk Al. Measured ultimate tensile strengths and yield points of Al coatings were comparable to those of bulk Al. This may be due to work hardening resulting from the plastic deformation necessary for coating formation. These tensile test results are consistent with coating cohesive strengths as measured by stud pull tests. Higher powder feed rates produced coatings with higher failure loads in three point bending, higher coating cohesion and lower coating strength anisotropy, presumably due to a peening effect. Four velocity-dependent stages of coating formation are proposed based on observations reported here. Coating properties arise from a competition between these stages. Parallels with models of dynamic (explosive) powder compaction are made. This is the first comprehensive model for kinetic spray coating formation.
TL;DR: In this paper, a single hole drilling and scanning procedure was used to investigate the influence of the particle size on the excitation process within the ICP, and it was shown that particle size distribution is dependent on the wavelength of the laser and the absorption behavior of the sample.
Abstract: Laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) has become one of the well-accepted analytical techniques for in situ trace element analysis and a large number of successful applications have shown its potential. Each commonly employed laser wavelength (1064, 266, 213, 193, 157 nm) leads to some degree of non-stoichiometric ablation, which makes quantification using non-matrix-matched calibration standards difficult for some elements. Time-dependent changes in elemental ratios (so-called elemental fractionation) have been ascribed mostly to processes occurring at the ablation site. Therefore, wavelengths and related irradiance are the major variables that have been used to study this phenomenon in detail. However, there are a large number of parameters that influence the ablation process, aerosol transport, and the excitation process within the ICP. Each process can contribute to elemental fractionation, making the
effects of each difficult to separate and to study in detail. The influence of the ICP as one possible source has not been studied thoroughly. The aim of this study was the determination of the source of elemental fractionation using a 266 nm Nd∶YAG laser ablation system. The sample transport system was designed to keep gas flows and plasma conditions constant. Various ablation procedures (single hole drilling and scanning) were tested to investigate the influence of the particle size on the excitation process within the ICP. Mineral wool was used to filter various fractions of the laser-induced aerosol to study signal behaviour as a function of the mass load of the ICP. Uranium and thorium, two elements with very similar properties (ionisation potential and concentration) in the NIST 600 Glass standard series, were used in particular to study ICP processes. It is shown that the particle size distribution is dependent on the wavelength of the laser and the absorption
behaviour of the sample. The 266 nm Nd∶YAG laser produces a particle size distribution which is significantly larger in comparison with aerosols produced using a laser wavelength of 193 nm. Signals related to the ablated volume show that the larger particle fractions are not completely vaporised and ionised in the ICP. Filtering certain particle fractions allows final stoichiometric excitation and ionisation, but is accompanied by a loss of 50–80% of the total signal. For single hole ablation, the particle size distribution becomes smaller with increasing depth of the crater. Therefore, scanning mode ablation (which takes place always at the surface) produces a constant supply of larger particles, which results in significantly higher matrix effects within the ICP, as shown by significant changes in the elemental ratio of U∶Th. These studies indicate that the secondary effect of incomplete aerosol or particle excitation within the ICP is the dominant process
influencing elemental fractionation during LA-ICP-MS. The effect was observed to be different for individual ICP sources and, therefore, the requirement for matrix-matched quantification in LA-ICP-MS remains instrument-dependent.
TL;DR: In this article, the surface energies of the Mo-edge and S-edge terminated surfaces of single-layer nanosize MoS2 particles are derived as a function of the chemical potential of sulfur.
TL;DR: In this article, small inorganic particles strongly enhance water-crude oil emulsion stability when interactions with asphaltenes promote particle adsorption at the oil−water interface.
Abstract: Small inorganic particles strongly enhance water−crude oil emulsion stability when interactions with asphaltenes promote particle adsorption at the oil−water interface. A variety of particle types have been studied to investigate the controlling factors for particle-stabilization effectiveness. Emulsion stabilities were determined by the extent of water resolved after centrifugation and the electric field required for emulsion breakdown. All particles used were hydrophilic and stabilized oil-in-water emulsions if small enough to be interfacially active. When dried and exposed to asphaltene-containing oil phases, the particles stabilized water-in-oil emulsions. Decreased extents of preadsorbed water, decreased particle sizes, and increased particle concentrations enhanced water-in-oil emulsion stability. Investigations with model emulsions showed that an intermediate state of asphaltene aggregation, near the point of incipient precipitation, is required for particle modification and emulsion stabilization....
TL;DR: In this article, both particle size and particle volume fraction were systematically varied to investigate their effects on the fracture behavior and the fracture toughness of a highly-crosslinked, nominally brittle, thermosetting unsaturated polyester resin.
Abstract: Micron- and nanometer-sized aluminum particles were used as reinforcements to enhance the fracture toughness of a highly-crosslinked, nominally brittle, thermosetting unsaturated polyester resin. Both particle size and particle volume fraction were systematically varied to investigate their effects on the fracture behavior and the fracture toughness. It was observed that, in general, the overall fracture toughness increased monotonically with the volume fraction of aluminum particles, for a given particle size, provided particle dispersion and deagglomeration was maintained. The fracture toughness of the composite was also strongly influenced by the size of the reinforcement particles. Smaller particles led to a greater increase in fracture toughness for a given particle volume fraction. Scanning electron microscopy of the fracture surfaces was employed to establish crack front trapping as the primary extrinsic toughening mechanism. Finally, the effects of particle volume fraction and size on the tensile properties of the polyester-aluminum composite were also investigated. The measured elastic modulus was in accordance with the rule-of-mixtures. Meanwhile, the tensile strength was slightly reduced upon the inclusion of aluminum particles in the polyester matrix.