Showing papers on "Particle published in 1986"
TL;DR: Optical trapping of dielectric particles by a single-beam gradient force trap was demonstrated for the first reported time, confirming the concept of negative light pressure due to the gradient force.
Abstract: Optical trapping of dielectric particles by a single-beam gradient force trap was demonstrated for the first reported time. This confirms the concept of negative light pressure due to the gradient force. Trapping was observed over the entire range of particle size from 10 μm to ~25 nm in water. Use of the new trap extends the size range of macroscopic particles accessible to optical trapping and manipulation well into the Rayleigh size regime. Application of this trapping principle to atom trapping is considered.
6,434 citations
TL;DR: In this paper, a detailed study of the phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential is presented. But it is not a detailed analysis of the colloidal glass phase.
Abstract: Suspensions of spherical colloidal particles in a liquid show a fascinating variety of phase behaviour which can mimic that of simple atomic liquids and solids. ‘Colloidal fluids’1–4, in which there are significant short-range correlations between the positions of neighbouring particles, and ‘colloidal crystals’5–7, which have long-range spatial order, have been investigated extensively. We report here a detailed study of the phase diagram of suspensions of colloidal spheres which interact through a steep repulsive potential. With increasing particle concentration we observed a progression from colloidal fluid, to fluid and crystal phases in coexistence, to fully crystallized samples. At the highest concentrations we obtained very viscous samples in which full crystallization had not occurred after several months and in which the particles appeared to be arranged as an amorphous ‘colloidal glass’. The empirical phase diagram can be reproduced reasonably well by an effective hard-sphere model. The observation of the colloidal glass phase is interesting both in itself and because of possible relevance to the manufacture of high-strength ceramics8.
1,881 citations
TL;DR: In this paper, the authors studied the settling and growth of dust particles in the subsequent laminar phase of the solar nebula in detail, treating a dust layer as a two-component fluid composed of the dust and the gas, and obtained analytic expressions for the settling path, the growing size, and the settling time.
628 citations
TL;DR: The mass spectra of cometary dust particles measured by the PIA dust particle analyzer aboard the Giotto spacecraft showed some unexpected and striking features as mentioned in this paper, such as small particles below 10 to the -14th g are much more abundant than anticipated by models.
Abstract: Mass spectra of cometary dust particles measured by the PIA dust particle analyzer aboard the Giotto spacecraft show some unexpected and striking features. First, small particles below 10 to the -14th g are much more abundant than anticipated by models. Second, most of the particles are rich in light elements such as H, C, N, and O, suggesting the validity of models that describe the cometary dust as including organic material. Third, the light elements specifically seem to have a low ratio of mass to volume. Three examples of original mass spectra showing typical compositions are given; these have been measured, and are compared with a computer-simulated mass spectrum.
411 citations
TL;DR: In this paper, the ion-aerosol attachment coefficients are calculated for Fuchs' theory and for a theory which includes three body trapping, and the resulting charge distributions agree quite well for particles with radii greater than about 0.007 μm.
Abstract: Calculations of the ion—aerosol attachment coefficients are carried out for Fuchs' theory (as corrected in this paper) and for a theory which includes three body trapping. The resulting charge distributions agree quite well for particles with radii greater than about 0.007 μm. For smaller particles three-body trapping becomes increasingly important. Comparison of theoretically predicted charge distributions with recently measured charge distributions at radii smaller than 0.02 μm show good agreement. Asymmetric charging due to differences in the physical properties of positive and negative ions can result in large differences in the number of positively and negatively charged particles, particularly at larger radii. The asymmetric charge distribution is also shown to depend on the ionization rate. For the case when aerosol concentrations are comparable to the ion concentrations the effect of polydispersity on the charge distribution is difficult to predict. It is shown that a dominant size particle can es...
383 citations
Patent•
03 Oct 1986
TL;DR: A magnetic-polymer particle, useful in immunoassay techniques and various other biological/medical applications is produced by coprecipitation of transition metals in the presence of a polymer having available coordination sites.
Abstract: A magnetic-polymer particle, useful in immunoassay techniques and various other biological/medical applications is produced by coprecipitation of transition metals in the presence of a polymer having available coordination sites. These particles are capable of forming stable aqueous suspensions and may be easily resuspended after agglomeration.
330 citations
TL;DR: In this paper, solidification synthesis of cast metal-ceramic particle composite materials by dispersing hard or soft ceramic particles (including microballoons) and short fibres in molten alloys before solidification is described.
Abstract: Solidification synthesis of cast metal-ceramic particle composite materials by dispersing hard or soft ceramic particles (including microballoons) and short fibres in molten alloys before solidification is described. Microstructures synthesized using a variety of casting techniques such as gravity or pressure die casting, centrifugal casting, and squeeze casting are discussed. Techniques to obtain a selected distribution of dispersed particles in cast alloy matrices by controlling solidification parameters and inducing melt particle wettability are reviewed. These cast metal-ceramic particle composites represent low cost, high performance, tailor made substitute materials for a variety of automotive and electromechanical applications such as pistons, cylinder liners, bearings, and current collectors, resulting in savings of material and energy.
300 citations
TL;DR: A theoretical model to investigate the role played by the particulate (two-phase) nature of blood on oxygen (O2) release in capillary-size vessels suggests that the fraction of total O2 transport resistance that resides inside the capillary is influenced significantly by the discrete nature ofBlood.
269 citations
TL;DR: In this article, the authors derived expressions for the concentration dependence of the effective self-diffusion coefficient for spherically symmetrical particles in colloidal systems using the cell model to describe the effect of varying concentration of colloidal particles.
Abstract: The self-diffusion of small molecules in colloidal systems is calculated using the cell model to describe the effect of varying concentration of colloidal particles. The relevant boundary conditions are found using arguments from the thermodynamics of irreversible processes. From a general description of the self-diffusion in systems with spherically symmetrical particles we derive expressions for the concentration dependence of the effective self-diffusion coefficientD
eff
for several cases of practical importance. It is shown that when the molecule studied is strongly attracted to the particle a minimum inD
eff
is expected around volume fractionΦ=0.35. It is also shown that the often made distinction between free and bound molecules is often problematic and a more general description is proposed. The obstruction effect generated by the excluded volume is discussed both for spherical and spheroidal systems. It is pointed out that the often used formula due to Wang ((1954) J Amer Chem Soc 76:4755) is incorrect for self-diffusion and for the obstruction factor for spheres we obtain (1+0.5Φ)−1. This expresion is tested both by experiments on water diffusion in systems containing latex particles and through computer simulations and it is found valid over a wide concentration range. For prolate ellipsoids the obstruction factor is not greatly different from that for spheres, while for oblate aggregates the limiting obstruction factor of 2/3 can be obtained at low concentrations. It is demonstrated that this effect can be used to distinguish between different aggregate shapes. It is also shown that the disorder present in a solution of colloidal particles leads to a decrease in the obstruction effect.
264 citations
TL;DR: A detailed investigation at the atomic level has been made of the factors affecting the dynamic activity of small gold crystals that are supported on thin films of amorphous carbon, silicon, and germanium.
Abstract: Small metal particles (<5 nanometers), which are widely used in catalysis, have physical and chemical properties that are markedly different from those of the bulk metal. The differences are related to crystal structure, and it is therefore significant that structral rearrangements in small particles have been observed in real time by using high-resolution electron microscopy. A detailed investigation at the atomic level has been made of the factors affecting the dynamic activity of small gold crystals that are supported on thin films of amorphous carbon, silicon, and germanium. The rate of activity depends mainly on the current density of the incident electron beam and the degree of contact of the particle with the substrate, but this rate decreases rapidly as the particle size is increased. The activity of the particles is very similar on either carbon or silicon, but it is generally less marked on germanium because of increased contact between the particle and the substrate. The electron beam effectively heats the particles, and it appears that their dynamic behavior depends on their thermal contact with the substrate.
260 citations
TL;DR: In this article, the authors applied novel methods to produce gold particle samples with their arrangements systematically varying from statistical disorder to densely packed particle aggregates of various mean sizes and shapes, and numerical calculations of explicit extinction spectra were performed on corresponding prototypic particle aggregate aggregates taking both interior and exterior retardation effects into account.
TL;DR: A particle interaction model is presented that assumes the existence of an additional desorption reaction that results from particle-particle interactions and is in conformity with the experimental results.
Abstract: The reversible component partition coefficient for nickel and cobalt sorbed to montmorillonite and quartz is shown to be a function of particle concentration. Resuspension and dilution experiments appear to exclude explanations that rely on nonseparated particles and/or complexing ligands associated with the particles. A particle interaction model is presented that assumes the existence of an additional desorption reaction that results from particle-particle interactions. The model is in conformity with the experimental results. The observed partition coefficient decrease with increasing ionic strength is a result of the decrease in the classical, low particle concentration limit, partition coefficient. The particle-particle interaction is independent of ionic strength. 41 references, 6 figures, 3 tables.
TL;DR: In this paper, the authors investigated the dielectric response of a colloid in which the particle radius a is much greater than the double-layer thickness κ −1 and showed that such colloids exhibit two types of dielectrics dispersion: one at frequencies of order D / a 2, and the other at higher frequency of order κ 2 D where D is the ion diffusivity.
TL;DR: In this paper, a parameterization scheme for the dry deposition of aerosol particles for use in tracer transport models is presented for smooth surfaces, surfaces with bluff roughness elements, ocean surfaces, and vegetative canopies.
Abstract: A parameterization scheme for the dry deposition of aerosol particles for use in tracer transport models is presented. Expressions of the particle deposition velocities relative to the bottom transport model level are derived for smooth surfaces, surfaces with bluff roughness elements, ocean surfaces, and vegetative canopies. The scheme is applied to a general circulation model to calculate the deposition velocities of ambient tropospheric aerosols. The calculated deposition velocities show a strong dependence upon the wind field in the bottom model level, the particle size distribution, and the surface type.
Patent•
25 Sep 1986TL;DR: In this article, high-dimensional spherical SiO 2 particles are produced by a two-step process where first a sol of primary particles is prepared by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous/alcoholic ammoniacal medium.
Abstract: Highly monodispersed nonporous spherical SiO 2 particles are prepared having mean particle diameters between 0.05 and 10 μm with a standard deviation of not more than 5% and a method for the preparation of such particles. The particles can be produced by a two step process wherein first a sol of primary particles is prepared by hydrolytic polycondensation of tetraalkoxysilanes in an aqueous/alcoholic ammoniacal medium. The SiO 2 particles are then converted to the desired particle size by a continuous measured addition of tetraalkoxysilane or organotrialkoxysilane controlled by the extent of the reaction. The SiO 2 particles produced by this process are particularly useful as sorption material in chromatography.
TL;DR: In this article, an experiment to search for the production of neutral penetrating particles decaying into electron-positron pairs was performed with a 2.5-GeV electron beam.
Abstract: An experiment to search for the production of neutral penetrating particles decaying into electron-positron pairs was performed with a 2.5-GeV electron beam. A total of 0.027 C was injected into a tungsten target. No such particle is found. Constraints on coupling constants ..cap alpha../sub e-italic/ and ..cap alpha../sub ..gamma../ are given.
TL;DR: In this paper, the authors showed that grain growth in polycrystalline caicite at 800°C and 300-MPa confining pressure is inhibited by the addition of Al2O3 particles; volume fractions of second phase (f) ranged from 0.02 to 10.0 vol%, and several powders with different average particle size were used.
Abstract: Grain growth in polycrystalline caicite (CaCO3) at 800°C and 300-MPa confining pressure is inhibited by the addition of Al2O3 particles; volume fractions of second phase (f) ranged from 0.02 to 10.0 vol%, and several powders with different average particle size were used. The stable grain size reached during heat treatment was inversely proportional to l/fm where m varied from 0.3 to 0.55 — agreeing with results from other grain growth experiments in ceramics and metals, and with models developed for particles located at grain boundaries and grain corners, but not agreeing with models developed for random dispersions. The dependence of the stable grain size on second-phase particle size in these experiments was less systematic, possibly because of variations in the particle size distributions used, or because of particle agglomeration effects. In the single-phase aggregates, the growth kinetics were consistent with a normal grain growth equation with n=3, although uncertainties were large.
TL;DR: In this article, the reactions of eaq− (CH3)2COH, and Cd+ with 3 nm CdS particles were investigated by pulse radiolysis, and the effect is explained by an increase in the energy of the excitonic state which is formed by light absorption.
TL;DR: In this paper, sterically stabilized poly(methylmethacrylate) (PMMA) particles were dispersed in silicone fluids of different viscosities, at concentrations up to 45% by volume.
TL;DR: In this article, NaY zeolites of varying average particle size were synthesized and incorporated into fluid cracking catalysts, which exhibited agglomeration and intergrowths, and the external surface area measured by N2 adsorption t plot was used to calculate effective particle size.
TL;DR: In this paper, the size distributions of giant sea spray particles (10-100 micrometer diameter) were measured in the North Atlantic with an impaction method, at heights of 0.2, 0.5, 1, 2, 4, 6, and 11 m above instantaneous sea level.
Abstract: Size distributions of giant sea-spray particles (10-100 micrometer diameter) were measured in the North Atlantic with an impaction method, at heights of 0.2, 0.5, 1, 2, 4, 6, and 11 m above instantaneous sea level. The vertical distributions of the particle concentrations show as characteristic features a minimum at 0.5 m at low winds, and at higher winds a maximum at 1-2 m. The windspeed dependence of particle concentrations is a function of both particle diameter and height above sea level. The results are explained by a qualitative model based on literature data on the production of sea-spray particles and on turbulent wind structure over water waves.-Author
TL;DR: Specific behaviour for fine particles seems to be attributed to the contribution of steric stabilization by the hydrated layer on the particle surface and to the inability for the leucocytes to recognize very fine particles as foreign materials.
TL;DR: In this article, the effect of UV illumination on the stability of ZnO particles in aqueous suspensions is investigated, and the quantity of the Zn(II) photodecomposed has been determined by measuring polarographically the resulting ZnII concentration in solution at different irradiation times, pH, and mass of semiconductor in suspension.
Abstract: The effect of UV illumination on the stability of ZnO particles in aqueous suspensions is investigated. The quantity of ZnO photodecomposed has been determined by measuring polarographically the resulting Zn(II) concentration in solution at different irradiation times, pH, and mass of semiconductor in suspension. The effect of different hole scavengers added to the solution in order to increase the stability of the semiconductor is also analyzed. Finally, some electrochemical measurements have been carried out with the aim to estimate the electron energy levels in the semiconductor particle under irradiation.
TL;DR: Particle coalescence in latex films is investigated by measuring the "smearing out process" of perdeuterated nPBMA latex particles in a matrix of protonated n PBMA using SANS as discussed by the authors.
Abstract: Particle coalescence in latex films is investigated by measuring the “smearing out process” of perdeuterated nPBMA latex particles in a matrix of protonated nPBMA using SANS. It is found that—at least in this system—there is massive interdiffusion of material of different latex particles. Diffusion constants for 70 °C and 90 °C tempering temperatures are determined. In addition, the effect of molecular mass, crosslinking and incompatibility of the matrix material is investigated. As expected, the interdiffusion decreases with increasing molecular mass, but, surprisingly, dense crosslinking of the matrix latex particles accelerates the smearing out process. Increasing incompatibility lowers the rate of the smearing out process.
TL;DR: In this paper, a review of the published data on such streaming motions is presented, which describes new visual and photographic observations of the evolution of the internal structures (which are sometimes more globular than columnar) in a large number of different bidisperse systems.
Abstract: It is known that when two different species of small particles with radii in the range 10–100 μm are dispersed uniformly in fluid and are settling under gravity, there may be a tendency for the particles of each species to gather together and develop a bulk vertical streaming motion, which results in much larger magnitudes of the mean velocity of at least one of the two types of particle. After a review of the published data on such streaming motions we describe new visual and photographic observations of the evolution of the internal structures (which are sometimes more globular than columnar) in a large number of different bidisperse systems. It appears that the observed structures result from instability of the statistically homogeneous dispersion to small concentration disturbances for certain combinations of values of the ratios of the sizes and densities of the two types of particle and the volume fractions of the two species.The condition for growth of a sinusoidal disturbance of the homogeneous dispersion is derived from the two particle-conservation equations and is found to involve the dependence of the two mean particle velocities on the two particle concentrations in a homogeneous dispersion. Previously calculated values of these mean velocities for a dilute dispersion suggest that the condition for instability is indeed satisfied for not-too-small particle concentrations and certain combinations of the size and density ratios of the two particle species. The results of the instability theory are generally consistent with the observed features of the structures, regarded as finite-amplitude forms of the small disturbances with maximum growth rate.
TL;DR: In this paper, a general method to describe the spectroscopy of large, internally inhomogeneous particles is presented, which utilizes an approach similar to the one used by DeVoe in the treatment of the optical properties of polymers.
Abstract: A general method to describe the spectroscopy of large, internally inhomogeneous particles is presented. The theory utilizes an approach similar to the one used by DeVoe in the treatment of the optical properties of polymers. The particle is divided into groups and the internal field is calculated by solving a self‐consistent set of linear equations in the field amplitude at each group in the particle. It is found that if the particle is dense the intermediate and radiation coupling mechanisms must be included in addition to the dipole–dipole coupling. Through these coupling mechanisms it is found that the excitation generated at each group in the chromophore can delocalize over regions comparable to the size of the wavelength of light. The response of the particle to the light can then be described in terms of ‘‘collective modes’’ of excitation of the entire particle, the amplitude of each mode being controlled by the geometrical relation between the groups and the efficiency in energy transfer between any two groups in the aggregate. The spatially averaged equations of the absorbance for a collection of large inhomogeneous arbitrarily shaped aggregates are derived.
TL;DR: In this paper, the effect of Brownian diffusion on the electrical classification of ultrafine particles in the differential mobility analyzer (DMA) has been studied theoretically and experimentally.
Abstract: Effect of Brownian diffusion on the electrical classification of ultrafine particles in the differential mobility analyzer (DMA) has been studied theoretically and experimentally. Two kinds of particle losses which are undesirable in size analysis, (1) loss caused by the Brownian diffusion of particles traversing the sheath air stream toward the collector rod of the DMA, and (2) loss caused by Brownian diffusive deposition of particles on every wall of the DMA excluding the collector surface, were theoretically evaluated by solving the diffusion equation. Some of the calculation results were confirmed by experiments for particles of various sizes, two different lengths of DMA and various ratios of flow rate of aerosol to sheath air.
TL;DR: In this paper, the principle of heterogeneous nucleation was used to develop a method for the preparation of homodisperse haematite hydrosols with extremely high turbidity.
TL;DR: In this paper, the effect of asphaltenes on the contact angle at the water/oil/solid interface and on the zeta potential of the particles was investigated, and the hydrophobic nature of the solids was found to be directly related to the amount of adsorbed on their surface.
TL;DR: Aerosol samples were collected on a Pacific cruise from 47°N to 55°S as mentioned in this paper, where particle morphology, concentrations, and size distributions were analyzed with an electron microscope; elemental compositions of individual particles were determined with an X-ray energy spectrometer; and chemical compositions of bulk samples were measured with an ion chromatograph.
Abstract: Aerosol samples were collected on a Pacific cruise from 47°N to 55°S. Particle morphology, concentrations, and size distributions were analyzed with an electron microscope; elemental compositions of individual particles were determined with an X-ray energy spectrometer; and chemical compositions of bulk samples were measured with an ion chromatograph. Temporal and spatial variations of aerosol physico-chemical characteristics were studied in relation to ocean currents and atmospheric parameters. The results show that number and mass concentrations of primary particles depend mainly on surface wind speeds. However the ratios between the major ions, e.g., Na+, Cl-, and Mg++, are similar to the ratios in seawater regardless of location or meteorological conditions. The concentrations of secondary aerosols, e.g., non-seasalt sulfate, nitrate, and ammonium particles, show maxima at upwelling regions, such as along the California coast, at the Equator, and near the Chatham Rise where ascending motion brings nutrient-riched deep water into the surface layer. The number concentrations of small sulfate particles and large nitrate-coated particles showed diurnal variations with maxima in the early afternoon and minima at night, indicating that the particles are the products of photo-chemical reactions. Their precursor gases, e.g., CH3SCH3, NO, and NH3 are known to be released from seawater in upwelling regions where biological activities thrive.