Dispersion Of Small Particles Research Articles

Morphology development during reactive and non-reactive blending of an ethylene-propylene rubber with two thermoplastic matrices

The development of morphology from pellet-sized particles to submicrometre droplets during the polymer-blending process is investigated for two pairs of polymer blends. The systems are blends of a rubbery phase in a glassy matrix, namely amorphous nylon/ethylene-propylene rubber and polystyrene/ethylene-propylene rubber blends. In each case the investigation is pursued for a non-reactive blend and a similar reactive blend where the phases may chemically react at the interface during the blending process. The dispersed phase particle size distribution is determined as a function of mixing time for these systems. The behaviour of the blends with matrices of nylon and polystyrene is qualitatively similar. The major reduction in the dispersed phase size is found to occur at short mixing times, in conjunction with the softening process. For example, in the case of a reactive nylon/ethylene-propylene rubber blend, the volume average particle diameter of the dispersed phase is reduced from ∼4 mm (pellet size) to ∼ 1 μm within the first 90 s of mixing. At intermediate mixing times, the morphology consists of a large number of small dispersed phase particles (which are about the same size as the particles observed in the final blend) along with a small number of very large particles which constitute most of the volume occupied by the rubber phase. The effect of subsequent mixing is primarily to reduce the size of the largest particles in the size distribution. The interfacial chemical reaction between the phases reduces the dispersed phase size and narrows the size distribution.

In vitro relaxometric characterization of superparamagnetic contrast agents

The relaxation behaviour of solvent protons of aqueous dispersions of single crystals, and of small agglomerates of superparamagnetic materials, has been measured at 0.47 T and 37 °C, and compared with that of larger systems like magnetic spheres or large agglomerates of magnetic grains. The longitudinal recovery of the nuclear magnetization, as well as its transverse decay, allow for mono-exponential fits only for dispersions of small particles, sized up to a few tens of nanometers. In this case the transverse relaxation rateR2 is independent of the echo time, and has a linear relationship to the iron concentration. For larger particles or agglomerates of a diameter lying within the micrometer range, the transverse evolution obtained with a Carr-Purcell-Meiboom-Gill (CPMG) sequence is characterized by a marked influence of the inter-pulse delay (TE), and has to be described by a multiexponential regime including a very fast initial decay. The initial fall in magnetization is one of the most prominent features of the large-size systems and, together with the parameters describing the subsequent multiexponential regime, is an important factor in the description of their effect. This parameter may be valuable in the comparison of such agents.

Multiphoton mechanism of generation of elementary excitations in disperse SiO 2

The generation of elementary electron excitations in small particles of SiO 2 under intensive infrared excitation ( λ exc = 1064 nm, F exc = 10 5 −2 × 10 8 W/cm 2, τ p = 20 ns) was examined. The analysis of these processes was based on the investigations of spectral-luminescence properties under multiphoton excitation of a dispersion of small particles of SiO 2. It was determined that the generation mechanisms of elementary electron excitations in such samples of SiO 2 are the photoionization process under multiphoton charge modification of defect centers and the generation of relaxed excitons in non-disturbed silica.

A spectral method for the numerical solutions of a kinetic equation describing the dispersion of small particles in a turbulent flow

In this paper we consider numerical solutions to a kinetic equation for the dispersion of small particles in a turbulent flow. The solution represents the probability density that a particle has a certain velocity and position at a given time. These solutions are based on a mixed finite-difference spectral method. Computational results are presented.

The dependence of the surface tension of surfactant solutions on drop size

It is shown that when the surface area of a surfactant solution is greatly extended by creating a dispersion of small particles (e.g., drops), the surface tension of the solution of which the particles consist depends on the particle size. This stems from the fact that the amount of surfactant in each particle is finite. Consequently, the distribution of surfactant between the bulk and the interface of a small particle is different from its distribution in the original solution. Calculations for SDS solutions demonstrate that the surface tension of drops appreciably deviates from that of the original solution for drops smaller than about 10 μm in radius. This size range coincides with that typical of aerosols and emulsions. For surfactants of higher surface activity, the effect of size on the surface tension is appreciable even for much larger drops.

A spectral method for the numerical solutions of a kinetic equation describing the dispersion of small particles in a turbulent flow

A spectral method for the numerical solutions of a kinetic equation describing the dispersion of small particles in a turbulent flow

Particle dispersion in the developing free shear layer. Part 2. Forced flow

An experimental investigation of the dispersion of small particles in a developing, high-Reynolds-number, turbulent, plane mixing layer is presented. Flow visualizations, laser attenuation and diffraction techniques as well as hot-wire anemometry are used to describe the evolution of the mean and instantaneous particle and gas flow fields. It is shown that the large scale turbulent motion existing in the mixing layer plays a central role in the dispersion of the particles. The mean particle concentration field is shown to be the result of a statistical distribution of streaks produced by the large-scale coherent component of the turbulent motion in the mixing layer. Furthermore, for every particle size, the spreading of the particle concentration thickness is found to occur at a smaller rate than the one characterizing the momentum of the turbulent carrier gas. Large particles are shown to initially disperse into the mixing layer less effectively than the small ones. However, when both downstream and cross-stream coordinates are non-dimensionalized with a characteristic length proportional to the square of the droplet diameter, a universal, particle-size independent dispersion field is found to exist.

Blends of sulphonated polystyrene and polystyrene: Morphology and deformation modes

AbstractBlends of sulphonated polystyrene, neutralized with metal ions, have been prepared in various proportions with polystyrene homopolymer. Morphology, microstructure, and deformation modes of strained, cast thin films have been examined by transmission electron microscopy. Variables studied include blend composition and ion content. In blends of low ionomer concentration, the ionomer component phase‐separates and takes the form of small dispersed particles. With the increase of ion content, the average particle size increases and, as crazes develop in the matrix, particles elongate and fibrillate. These ionic crosslinked particles adhere well to the matrix, share in carrying the applied stress and reinforce the matrix polymer. Implications of these results for mechanical performance of bulk samples are discussed.

Distribution of magnetic flux in high-Jc YBa2Cu3O7 superconductors

We present high-resolution Bitter patterns which reveal the flux distribution in high-Jc melt-textured growth superconductor YBa2Cu3O7 at 64K. Glass type of spatial configuration of vortex was observed and it supports the vortex glass model. In addition to the conventional pinning sites, such as twin boundaries, grain boundaries, microcracks etc., the dispersed small particles, ≤0.5μm in size, of the second phase also cause flux pinning. The strongest pinning appears in the vicinity of large grains of second phase, where the crystal lattice is seriously distorted.

The preparation and properties of dispersions of electrically-conducting polypyrrole particles

A conventional aqueous dispersion polymerisation technique has been used to prepare polypyrrole latices having particle diameters in the size range 300–450 nm and conductivities as high as 2–3 S cm −1. Both FeCl 3 and (NH 4 2S 2O 8 have been used as initiators. High M w PEO has been used as the steric stabiliser; this may be subsequently removed to give bare polypyrrole particles dispersed in water. Much smaller polypyrrole particles ( < 70 nm) may be prepared using an inverse microemulsion polymerisation procedure with the initiator in one set of dropelts and the monomer in the other. On quenching the reaction, by diluting the microemulsion into an aqueous solution of polyvinylpyrrolidone (stabiliser), stable dispersions of small particles may be prepared. Electrophoretic mobilities, as a function of pH, and various background KCl concentrations, have been determined. The “bare” particles show an isoelectric point which depends on the initiator used. Adsorption isotherms for sodium poly (styrene sulphonate) onto the bare latices (at low pH) have also been established. Effects arising from the bulk charge density, as well as the surface charge density, may play a role. Finally, critical electrolyte (KCl) concentrations for coagulation of the “bare” particles have been found; these are very low compared to the values found, e.g., for polystyrene latex. Calculations of the zeta potentials from mobility data imply that, for the purpose of electrophoresis, conducting particles should be treated as “insulators” (confirming a suggestion made by Overbeek some 40 years ago). Finally, Hamaker constants for the polypyrrole particles have been established which agree well with those predicted for metals.

Downward flux of zooplankton fecal pellets in the upper 2,000 m water column of the Izu Trench, western North Pacific

Sinking particulate matter were obtained from twelve depths using free-drifting sediment trap arrays which were deployed in the upper 2,000 m water column of the Izu Trench, northwest Pacific Ocean. The largest flux of 146 mgC m−2 day−1 was observed at 150 m depth. The flux generally decreased with depth below the maximum, however, minor flux peaks occurred at 1,000 and 1,250 m depth (>30 mgC m−2 day−1). Sinking large particles (>100 µm) were composed of fecal pellets typical of crustaceans, macroscopic aggregates, and planktonic organisms and their fragments. Three major components constituted 19%, 20% and 29%, respectively, of the total carbon flux (averaged from the fluxes at five depths; 50, 100, 150, 1,000 and 2,000 m). Among them, fecal pellet flux and large organism flux were well correlated with the total flux. The close correspondence between the fecal flux and the total carbon flux suggests that the latter is derived from a group of variables including other biogenic matter, among which fecal pellet is one of the leading factors controlling total flux, though the latter is only a minor covariable in quantity. Vertical flux profiles of fecal pellets and their internal constituents revealed some new inputs of feces occurring through the water column. This phenomenon implies that downward transportation of organic material is characterized by feeding and egestion activities of zooplankton, including overlapping processes of sinking and dispersion of large fecal particles and repackaging of dispersed small particles.

Properties of metal clusters in polymerized hydrocarbon versus fluorocarbon matrices

The ability to produce transition-metal clusters dispersed in a polymeric matrix by metal sputtering and plasma polymerization in a rf capacitively coupled diode reactor svstem was investigated. An in situ plasma diagnostic technique, i.e., optical emission spectroscopy, was used to predict the metal concentration of the film. Characterization of metal-containing plasma-polymerized propane thin films was realized using x-ray photoelectron spectroscopy, x-ray fluorescence, Raman spectroscopy, transmission electron microscopy, and electron diffraction. Evidence is given that the metal is present in its metallic state in the organic matrix and in the form of uniformly dispersed small particles. The shape and size of gold and cobalt particles at equivalent volume fractions are shown to be different, which is reflected in different electrical percolation threshold values for the two systems.

On the irrelevance of phase size in purification

Recently, Reis has suggested that it might be possible to remove a solute species completely from a small (or finely dispersed) phase by a reduction to some low but finite value of the chemical potential of that species in the medium surrounding the phase. Sciamanna and Prausnitz, while expressing some doubts about the rigor of the theoretical approach, used similar arguments to examine the possibility of obtaining ultrapurity in a small dispersed phase by equilibrium purification operations such as distillation and extraction. Here they demonstrate that Reis' original suggestion is incorrect. Furthermore, they show that, under well-defined and reasonable assumptions, the size of a phase has no influence on its purity.

Processing‐morphology relationships of compatibilized polyolefin/polyamide blends. Part I: The effect of an lonomer compatibilizer on blend morphology

AbstractThe morphology of compatibilized polyolef in/polyamide blends was found to be significantly dependent on the concentration of an ionomer compatibilizer (polyethylene‐methacrylic acid‐isobutyl acrylate terpolymer) in the blend. For a dispersed phase content of 10% by weight, a maximum reduction in phase size was observed when only 0.5% by weight of ionomer was added to the blend, A more significant reduction of the dispersed phase size was observed when the minor phase was nylon, due to interactions which exist between the ionomer and the polyamide. These interactions have been confirmed by Fourier transform infrared spectroscopy. At high concentrations of the ionomer, flocculation of the nylon dispersed phase was observed. In comparison to one‐step mixing, blends prepared by two‐step or batch mixing were characterized by a smaller dispersed phase when nylon was the matrix, and a larger particle size when nylon was the minor phase. The results observed are explained in terms of a speculative model of the interactions occurring across the nylon‐polvolefin interface.

Compositional and morphological analysis of AgCl films deposited by evaporation and R.F. sputtering

AgCl thin films in a range of thicknesses from 0.05 to 2 μm were deposited by evaporation and r.f. sputtering of AgCl as well as by co-evaporation of AgCl and silver. Their structure and composition were studied using X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, Auger electron spectroscopy, energy-dispersive X-ray analysis and optical absorption spectroscopy. Films grown by evaporation show a preferential grain orientation that depends on the deposition rate. They are stoichiometric except for chlorine enrichment at the surface, but exposure to an electron beam or UV light causes metallic silver formation. AgCl films grown by r.f. sputter deposition have greater surface roughness than those grown by evaporation, a random grain orientation and a grain size that depends on the sputtering conditions. Metallic silver is present in these films. Optical absorption measurements of co-evaporated films suggest that the metallic silver occurs in two forms, small dispersed particles in the AgCl matrix and larger particles at the grain boudaries.

石炭貯蔵時の炭じん飛散および自然発火

Coal dust emission from and spontaneous combustion of coal storage piles are becoming problems of increased importance as the volume of coal used and stored is expanding. Research results concerning these problems and preventive measures are summarized as follows:1. Coal dust emission is caused by dispersion of small particles of diameters less than 200 micrometers from coal piles. Methods for predicting coal dust emission quantities during operational storage were developed. Also, effectiveness of control methods including water sprays and wind shields were assessed.2. Spontaneous combustion of coal is caused by low temperature oxidation of coal. It was observed that pile temperatures must rise to 80 to 90 degrees C and be maintained for a period of time for spontaneous combustion to occur. A system using infra-red imaging apparatus was developed to predict the probability of spontaneous combustion in coal piles.

Dispersion of small particles on carbon surfaces

The formation of small solid particles (metals or metallic derivates) on carbon supports are discussed in relation to the surface properties of the carrier. In the case of graphitized carbons, the degree of dispersion of the supported solid increases with the content of prismatic or edge planes of the carbon substrate. Finely dispersed solids are obtained when the support solid or its precursor interacts with the carbon atoms of the edge planes. The sintering behaviors of supported solids are discussed in relation to the surface properties of the carbon and the environmental conditions.

The recrystallisation of aluminium-silicon alloys containing a bimodal particle distribution

The recrystallisation behaviour of Al-Si alloys containing bimodal dispersions of silicon particles was studied using optical and transmission electron microscopy. This behaviour was compared with that of several unimodal alloys with different particle dispersions. For the bimodal alloys, the large particles were observed to act as nucleation sites. The overall kinetics of recrystallisation however, were retarded due to the influence of the fine dispersion of small particles, and were similar to those of an alloy containing small particles only. It was concluded that the fine dispersion primarily affected the early stages of nucleus growth. The recrystallised grain size and shape were found to be dependent on the annealing temperature, and the fine dispersion level.

On the dispersion of small particles suspended in an isotropic turbulent fluid

A solution to the dispersion of small particles suspended in a turbulent fluid is presented, based on the approximation proposed by Phythian for the dispersion of fluid points in an incompressible random fluid. Motion is considered in a frame moving with the mean velocity of the fluid, the forces acting on the particle being taken as gravity and a fluid drag assumed linear in the particle velocity relative to that of the fluid. The probability distribution of the fluid velocity field in this frame is taken as Gaussian, homogeneous, isotropic, stationary and of zero mean. It is shown that, in the absence of gravity, the long-time particle diffusion coefficient is in general greater than that of the fluid, approaching with increasing particle relaxation time a value consistent with the particle being in an Eulerian frame of reference. The effect of gravity is consistent with Yudine's effect of crossing trajectories, reducing unequally the particle diffusion in directions normal to and parallel to the direction of the gravitational field. To characterize the effect of flow and gravity on particle diffusion it has been found useful to use a Froude number defined in terms of the turbulent intensity rather than the mean velocity. Depending upon the value of this number, it is found that the particle integral time scale may initially decrease with increasing particle relaxation time though it eventually rises and approaches the particle relaxation time. It is finally shown how this analysis may be extended to include the extra forces generated by the fluid and particle accelerations.

Sex differences in human urinary steroid metabolic profiles determined by gas chromatography

Fifty-two 24-hr urine collections from healthy male and female adults were analyzed by a new gas chromatographic method. High-resolution open tubular glass capillary columns with a coating of SE-30 liquid phase containing a dispersion of small particles of silanized silicic acid (Silanox) were employed. The components were analyzed as methoxime-trimethylsilyl ether derivatives. Seventeen urinary steroid metabolites were quantified through use of an internal reference compound. The results are interpreted as delineating two different types of steroid metabolism for premenopausal females: one group displays metabolic profiles closely resembling those of males. The biologic origin of this effect is not known, but it may be due to either late fetal or neonatal hormonal effects.