Dielectric Behavior of Oblate Spheroidal Particles:Application to Erythrocytes Suspensions

We have investigated the pressure effect on the eletrorotation (ER) spectrum of living cell suspensions byconsidering the particle shape effect. In particular, we consider coated oblate spheroidal particles and present a theoreticalstudy of ER based on the spectral representation theory. Analytic expressions for the characteristic frequency as wellas the dispersion strength can be obtained, thus simplifying the fitting of experimental data on oblate spheroidal cellsthat abound in the literature. From the theoretical analysis, we find that the cellshape, coating as well as materialparameters can change the ER spectrum. We demonstrate a good agreement between our theoretical predictions andexperimental data on human erthrocytes suspensions.     

Dry Mechanical Dispersion of Submicron Particles

Concerning the use of air classifiers with cut sizes in the micron range and lower, it is necessary to disperse the feed material properly in an air flow to avoid agglomerates larger than the desired cut size. Commonly used dispersing devices such as injectors use large amounts of air. To reduce the size and costs of the subsequent air classifiers, two new types of dispersing systems were developed, one design being related to a brush feeder and the other to a pin mill. Both apply mechanical rather than fluid mechanical forces in the dispersion process. The brush disperser achieves the same size distributions as the pin mill disperser with much less machinery. Its properties as a feeding and dispersing system are shown and its ability to disperse particles in the submicron range is confirmed by two independent particle size analysis systems: a new diffraction spectrometer and an impactor.     

Study on Steady Shear Rheological Behavior of Concentrated Suspensions of Sulfonated Polyacrylamide/Na-Montmorillonite Nanoparticles

Concentrated suspensions of sulfonated polyacrylamide (SPA)/Na⁺-montmorillonite (Na-MMT) were prepared and their stability and steady shear rheological properties were described as a function of nanoparticle and polymer concentration and temperature. The results showed that the Na-MMT nanoparticles suspensions were stable in the absence and presence of SPA and no sedimentation was seen. The Z-average particle sizes for the SPA/Na-MMT suspensions increased in the presence of SPA. Rheological investigations showed that the SPA solutions and SPA/Na-MMT suspensions displayed non-Newtonian behavior in almost the whole range of shear rate. All the suspensions exhibited a shear-thinning flow character as shear rate increased. The flow curves indicated the shear viscosity and stress of the samples were decreased with increasing nanoparticles concentration up to 1.5 wt%, but for Na-MMT loading greater than 1.5 wt% there was an increase in shear viscosity and stress of the suspensions. Increasing of SPA concentration had more effect on increasing the rheological properties of SPA/Na-MMT suspensions than increasing of nanoclay content. Shear viscosity and stress of the suspensions increased with increasing SPA concentration and decreased with increasing temperature from 50°C to 70°C.     

Ultrasonic Spectrometry for Particle Size Analysis in Dense Submicron Suspensions

Ultrasonic spectrometry was applied to the particle size analysis of disperse systems. The investigations were made for acoustic conditions called the long-wavelength regime (LWR). In the LWR the acoustic behaviour is governed by dissipative effects rather than by scattering. Two principal theoretical approaches to ultrasonic spectrometry — scattering theory and coupled phase models — are introduced. A model based on a newly developed coupled phase model and the scattering theory (ECAH theory) is implemented in the ultrasonic spectrometer Acousto Phor. Experiments were carried out for several suspensions with a high density contrast. It could be demonstrated that the model successfully describes acoustic attenuation and that the inversion algorithm finds particle size distributions comparable to those given by other measurement techniques. With regard to the particle size, a lower and an upper limit for the applicability were determined, which include three decades. As a further result, the model was validated at concentrations up to 10 vol.%. The model is considered to be open to development to cover even higher concentrations.     

In-line FBRM Monitoring of Particle Size in Dilute Agitated Suspensions

The use of laser light scattering technology, as applied by the Focused Beam Reflectance Measurement (FBRM) probe from Lasentec, for the in-line monitoring of particle size was investigated. In particular, the effects of probe position and orientation were studied for a dilute agitated aqueous particulate suspension of known particle size distribution in a number of vessels. In all cases, the normalised chord length distribution recorded with the FBRM system was consistent with the theoretically predicted distribution. However, the total number of counts measured was a function both of solids concentration and probe location. Optimum probe location is dependent on the ease with which the solid phase can be suspended with the available agitation system and on the associated dominant flow direction within the vessel.     

Formation of Submicron Zinc Particles by Electrodeposition

The influence of the cationic composition on the electrochemical deposition of zinc on plane cathodes was investigated. Electrochemical deposition of zinc from aqueous feed needs high purity of the feed electrolyte owing to sensitivity of the hydrogen overvoltage. In contrast to sulfate‐based electrolytes, the hydrogen overvoltage in acetic acid can be kept high in electrodeposition of zinc and several heavy metals such as nickel. As a consequence, electrochemical deposition of zinc is possible even at nickel concentrations of 50 mg/l and above. Depending on the electrolyte composition in acetate‐based systems the deposition of granular zinc of different particle size, from the micron to the submicron range, is possible on plane electrodes. The chemical composition of granular deposits from several acetate‐based electrolytes was analysed by inductively coupled plasma (ICP) analysis and their structure and morphology were detected by scanning electron microscopy (SEM) and energy‐dispersive X‐ray spectrometry (EDXS).     

An Electroacoustic Investigation of Concentrated Aqueous Suspensions of Calcium Pyrophosphate

The zeta potential of concentrated suspensions of calcium pyrophosphate were investigated using electroacoustics. The particles were negatively charged over the entire pH range studied. It proved impossible to reduce the pH of the suspension below 1.8, but the iso electric point could be estimated to occur at approximately pH 1. Two commercially available dispersants (one cationic and one anionic) were then added in small increments to the suspension in order to follow the change in zeta potential as the dispersants adsorbed onto the particles. From the shape of the curve it was possible to estimate the optimum adsorbed amount of dispersant required to fully coat the particles. The cationic dispersant adsorbed strongly and the optimum dosage was estimated at 2.5 ml of active polymer/kg of powder. Anionic dispersants are known to adsorb onto negatively charged ceramic oxide particles, but the anionic dispersant used in this study did not adsorb onto the negatively charged calcium pyrophosphate particles.     

Spectral Monitoring of Naftifine Immobilization into Submicron Vaterite Particles

Optics and Spectroscopy - Development of novel drug delivery systems providing the enhanced accumulation of the therapeutic agents in the area of pathology reducing in the meantime the systemic...     

Spin Exchange Between Charged Paramagnetic Particles in Dilute Solutions

Kinetic equations for the spin density matrix which take into account binary collisions and a method of calculating the spin exchange effective radius have been generalized to the case of dilute solutions of charged paramagnetic particles. The effective radius of the spin exchange and rate constant of the bimolecular spin exchange between charged paramagnetic particles in solutions have been calculated numerically. Calculations have been performed under the assumption that the exchange interaction is isotropic and decays exponentially with the increase in the distance between radicals, and the solution has a given dielectric permittivity and Debye screening radius. Dependences of the spin exchange rate constant on the mutual diffusion coefficient, exchange and electrostatic interactions parameters have been found numerically. The theory has been applied to experimental results taken from the literature. The rate constant of the spin exchange between radicals of like charge found from the experiment and calculated within the developed theory are in good qualitative agreement .     

Transmission Fluctuation Spectrometry in Concentrated Suspensions Part Two: Particle Overlapping

Transmission fluctuations measured on a flowing suspension of particles with a high spatial and temporal resolution can be used to measure the particle size distribution and particle concentration. The theory of transmission fluctuation spectrometry (TFS) was recently developed, whereby the statistical behavior of the entire suspension is described on the basis of a single monolayer, in combination with a layer model describing the suspension as a series of independent monolayers. As the monolayers are assumed to be statistically independent from each other, the transmission through the 3‐dimensional suspension is modeled as the product of transmissions through the monolayers.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions. Part Three: Measurements

The theory of transmission fluctuation spectrometry (TFS) was developed for particle size analysis in flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution (PSD) and particle concentration. In the previous parts of this publication high concentration effects on TFS were investigated theoretically and by simulation. This work presents a study on TFS measurements in concentrated suspensions. By introducing an empirical correction to include the high concentration effects from both the monolayer structure and particle overlapping in the inversion algorithm, it is possible to obtain the particle size distribution and particle concentration over broad ranges of particle sizes and concentrations.     

Monitoring the Dynamics of Concentrated Suspensions by Enhanced Backward Light Scattering

The shear-induced flocculation of kaolin-polymer flocs in a stirred tank is investigated at medium to high solids concentrations (ϕ=1−10% w/w). The evolution of the average floc size is monitored by the change in intensity of laser light scattered in the 180° direction. The measurements reflect the change in particle number concentration as flocculation proceeds. As flocculation begins, coagulation dominates and the floc size increases (total particle number decreases) and then levels off at a steady state value as fragmentation becomes significant and balances coagulation. At steady state, the measurements indicate the extent of flocculation. Increasing the shear rate increases the coagulation and fragmentation rates, resulting in smaller floc sizes at steady state. Increasing the flocculant concentration increases the steady state floc size by strengthening the bonds between primary particles to resist fragmentation. At constant shear rate and flocculant concentration, increasing the solids fraction decreases the steady state floc size indicating formation of weakly bonded flocs. Flocculant mixing was the most important factor for flocculation efficiency at high solids concentrations.     

Sizing of Submicron Aerosol Particles by the Whisker Particle Collector Method

Samples of an alumina powder aerosol were collected on whisker particle collectors and analysed following an improved evaluation scheme which allows the empirical size distribution to be corrected for the effect of a non-uniform collection efficiency. The measurement results are given in terms of log-normal distribution functions. Some ambiguity was encountered in interpreting particle aggregates that were found on the whisker collectors. By including the results of laser light-scattering experiments in the size analysis, this ambiguity was removed. Advantages and disadvantages of the whisker collector concept compared with light-scattering methods are discussed.     

Transmission Fluctuation Spectrometry in Concentrated Suspensions Part One: Effects of the Monolayer Structure

The theory of transmission fluctuation spectrometry (TFS) was recently developed for particle size analysis in dilute flowing particle suspensions, whereby the statistical transmission fluctuations are used to extract the particle size distribution and particle concentration.     

Surface Critical Behavior of Two-Dimensional Dilute Ising Models

Ising models with nearest neighbor ferromagnetic random couplings on a square lattice with a (1, 1) surface are studied, using Monte Carlo techniques and a star-triangle transformation method. In particular, the critical exponent of the surface magnetization is found to be close to that of the perfect model, Β₁ = 1/2. The crossover from surface to bulk critical properties is discussed.     

微米级高聚物包埋型金属铁复合粒子的球磨法制备及其磁流变效应

采用球磨法,能成功地直接从高聚物与金属铁的混合研磨中,获得微米级由聚苯乙烯和 甲基丙烯酸甲酯等高聚物包埋型金属羰基铁复合粒子。详细讨论制备条件包括不同高聚物比例、球磨时间对复合粒子形貌和粒径的影响及其复合粒子的热稳定性,还简要研究了由这些粒子组成的浓有机悬浮溶液的磁流变效应及其粒子的沉降稳定性。     

超细金属铁颗粒的高分子修饰及其悬浮液的磁流变性能

报道了γ射线辐照方法合成具有良好分散性的高分子复合金属铁粒子，分别选择十二烷基硫酸钠、溴化十六锘三甲基胺、Ｔｗｅｅｎ－８０、ＴｒｉｔｏｎＸ－２００和ＯＰ－１０表面活必睡有机单体、无机铁颗粒一起制备乳状液，通过对这种含有超细金属铁颗粒乳状液稳定性的比较，以寻求合适的乳化剂，并对以ＴｒｉｔｏｎＸ－２００为乳化剂时合成出的高聚物复合铁颗进行了ＸＲＤ、ＴＥＭ和ＩＲ表征，还将实验中所获得的高聚物复合铁粒子与