Particle size analysis by transmission fluctuation spectrometry with band-pass filters

The transmission fluctuation spectrometry (TFS) is a recently-developed method for real-time, online/inline particle analysis in two-phase flows, whereby the particle size distribution (PSD) and particle concentration can be measured simultaneously. This study presents a new technique of data processing to the fluctuating transmission signal. Instead of low-pass filters, band-pass filters are employed to improve the resolution of the measurement on particle size distribution. Based on the layer model, an analytical expression of the spectrum of the fluctuating transmission through a monolayer is derived and hence the spectrum of the fluctuating transmission through a 3-dimensional suspension is formulated. The comparison between simulation and theory at low concentrations shows a satisfactory match. Measurements on a mono-modal suspension are presented. It is found that the measurements using band-pass filters are of better resolution in the PSD than those with low-pass filters.     

Application of rayleigh spectroscopy to the study of emulsion and dispersion polymerization and polymers

Application of Rayleigh spectroscopy for characterization of particle size in nonaqueous dispersion and water-based emulsion paint resins is described. The technique allows a straightforward and rapid estimation of particle size; the measurement does not require exact determination of scatterer concentration. For monodisperse samples, unambiguous results are obtained for particles at least up to 50 μm in diameter; for polydisperse samples, an average size heavily weighted by large particles is obtained. Typical experimental results on monodisperse and polydisperse water-based latexes and on polydisperse nonaqueous dispersion resins are described. In the latter case, comparison of electron micrograph and light scattering size determinations indicates that the light scattering experiment yields approximately a z-average radius. Observations on particle formation and growth during polymerization are also described.     

三维有序二氧化硅胶粒膜在垂直基片上的自组装

A method for preparation of particle crystal film constructed trom monodisperse silica colloidal partices in diameter of about 300 nm is reported. The films were prepared from an ethanol suspension by vertical deposition that relies on capillary forces to assemble colloidal crystal particles on a vertical substrate. The 3D ordered films were characterized by transmission spectra and scanning electric microscope (SEM). The effect of evaporation temperature, particle concentration and sintered temperature on the quality of colloidal particle crystal film was investigated.     

Aerosol measurement by laser doppler spectroscopy—I. Theory and experimental results for aerosols homogeneous

The basic theory, experimental techniques and results are presented describing a technique for sizing aerosol particles in situ using laser Doppler spectroscopy. Unlike conventional light scattering procedures which use average intensity information, this technique utilizes the Doppler shifted frequency of the scattered light produced by the Brownian motion of the aerosol particles to determine particle diffusion coefficients and size. Experiments were carried out using monodisperse dibutylpthalate aerosols and monodisperse polystyrene latex spheres, in concentrations ranging from 10³ to 10⁶ particles per cubic centimeter. Measured particle sizes were within 10 per cent of the size predicted by conventional light scattering methods for the DBP particles and the reported sizes of the PSL particles. Based on these results it is concluded that laser Doppler spectroscopy can be utilized to accurately measure aerosol particle size in situ.     

Absolute Mass and Size Measurement of Monodisperse Particles Using a Modified Millikan's Method: Part I—Theoretical Framework of the Electro-Gravitational Aerosol Balance

A new method for accurate mass and size measurement of monodisperse particles is proposed. In this method, charged aerosol particles are introduced into parallel plate electrodes similar to the Millikan cell, and the number of particles left suspended after a certainty holding time has elapsed is measured. The particle survival rate as a function of the voltage applied to the electrodes is used to determine the particle mass. The particle size is deduced by using the particle density which is determined in a separate experiment. The expression of the particle survival function, which is defined as the survival rate as a function of the mass, for particles with and without Brownian diffusion is derived. The sensitivity of this method to the number average diameter, as well as other size distribution parameters, is analyzed on the basis of the survival function.     

A simple bimodal model for the evolution of non-spherical particles undergoing nucleation,coagulation and coalescence

A simple and efficient particle dynamics model is developed accounting for simultaneous nucleation, coagulation, and coalescence or sintering of non-spherical particles. In this model two discrete monodisperse modes are used to represent the non-spherical particle size distributions approximately: a size-fixed nucleation mode and a moving accumulation mode. The size-fixed nucleation mode accounts for the introduction of newly generated particles and the moving accumulation mode characterizes the particle growth by coagulation and coalescence. The simulation results for titania particle formation and growth using the proposed bimodal model are compared with those using the previous monodisperse non-spherical particle dynamics model and non-spherical polydisperse sectional model. The present bimodal model results in a very good agreement with the polydiserse sectional model even when particle nucleation coexists with coagulation process while the monodisperse model shows significant differences. It successfully predicts the morphological change of the non-spherical particles by coalescence. The present model is also shown to be capable of predicting the polydispersity of non-spherical particle distribution. The present non-spherical bimodal model requires the same level of the computation time that the simple monodisperse model does.     

Spatial gradients in particle reinforced polymers characterized by X-ray attenuation and laser confocal microscopy

The goal of this work is to develop techniques for measuring gradients in particle concentration within filled polymers, such as thermosetting polymer encapsulants. A high concentration of filler particles is added to such materials to tailor physical properties such as thermal expansion coefficient. Sedimentation and flow-induced migration of particles can produce concentration gradients that are most severe near boundaries. Therefore, techniques for measuring local particle concentration should be accurate near boundaries. Particle gradients in an alumina-filled epoxy resin are measured with a spatial resolution of 0.2 mm using an X-ray beam attenuation technique, but an artifact reduces accuracy near the specimen's edge. Local particle concentration near an edge can be measured more reliably using microscopy coupled with image analysis. This is illustrated by measuring concentration profiles of glass particles having 40 μm median diameter using images acquired with a confocal laser fluorescence microscope. The mean of the measured profiles of volume fraction agrees to better than 3% with the expected value and the shape of the profiles agrees qualitatively with simple theory for sedimentation of monodisperse particles. Evidence that the microscopic method can be extended to smaller particles is provided by local concentration measurements on an epoxy polymer containing particles having diameters of the order of 1 μm.     

The effect of polydispersity on dust lifting behind shock waves

Knowledge-based modeling of dust lifting behind shock waves is a prerequisite for realistic simulation of dust explosions. Mostly numerical simulations of this process focus on dusts consisting of monodisperse particles, while real dusts are polydisperse. This article investigates the effect on the lifting process of the dust being polydisperse with a log–normal distribution of particle sizes. The spatial distribution of the various sizes in the rising layer is studied, and statistical results for the rise, the collision frequency and the particle kinetic energy are compared for polydisperse and monodisperse dusts. It is shown that a layer consisting of polydisperse particles rises significantly faster than a one consisting of monodisperse particles, all other parameters being the same.     

Particle size distribution analysis by scattered light measurements using an optically defined measuring volume

This work describes an extended scattered light measuring system, with which the scattered light signals of all “border” particles can be recognized and eliminated. In addition to eliminating “border zone” errors, the apparatus permits improvements with respect to the possible measurement range, the maximum permissible particle concentration and the unambiguity of the scattered light signals for irregularly shaped particles.     

Measurements of Kelvin-Equivalent Size Distributions of Well-Defined Aerosols with Particle Diameters > 13 nm

During the 1979 workshop of the working group on ultrafine aerosols, different experimental techniques for measuring the number concentration and size of ultrafine aerosol particles were compared. In the present paper we report on a comparison of different particle size measuring techniques for ultrafine aerosols. Well-defined monodisperse aerosols with electrical mobility particle diameters ranging from 13 to 100 nm were generated using an electrical aerosol classifier. Kelvin-equivalent size distributions of these aerosols were determined by means of a process-controlled expansion chamber, the size-analyzing nuclei counter (SANC). To this end the considered aerosol was humidified and the number concentration of the droplets growing in the expansion chamber was measured for stepwise increase in supersaturation. At a quite well defined critical supersaturation, a significant increase in the measured droplet concentration, and thus the onset of heterogeneous nucleation, was observed. By means of the Kelvin-Gibbs equation this critical supersaturation is related to the Kelvin-equivalent diameter of the aerosol particles. Measurements were made on NaCl and dioctyl phthalate (DOP) aerosols. For NaCl particles the Kelvin diameter was found to be larger by a factor of about 4 than the electrical mobility diameter, as determined by the electrostatic aerosol classifier. This is explained by the solubility of the NaCl particles. For DOP particles, however, the Kelvin diameter agrees quite well with the electrical mobility diameter. The Kelvin size distributions were found to be quite narrow, indicating a high monodispersity of the generated aerosol as well as a satisfactory size resolution of the SANC. Thus different experimental techniques, based on completely different principles, yielded similar measurement results.     

Multiangle Polarimetry of Thermal Emission and Light Scattering by Individual Particles in Airflow

The generalized Kirchhoff's law predicts that the polarization state of thermal emission from an individual small particle depends on the particle shape. We show for the first time experimental evidence confirming this prediction for particles smaller than the wavelength by using a newly developed laser-induced incandescence instrument and a theoretical model that can predict the signals of thermal emission and light scattering for an ellipsoid under the dipole approximation (Rayleigh ellipsoid). We use single-sphere (singlet) and two-sphere clusters (doublet) of polystyrene latex spheres as primary test particles. These are currently available, well-characterized spherical and nonspherical particles, respectively. The polarization states of thermal emission and scattered light of graphite particles smaller than the wavelength show a good agreement with model calculations for plate-like Rayleigh-spheroids, consistent with their plate-like shapes observed by a transmission electron microscope. We propose that the measurement of the polarization state of thermal emission may be applicable to real-time analysis of the shape of light-absorbing particles in air.     

Intercomparison of Four Methods to Determine Size Distributions of Low-Concentration (∼ 100 cm−3), Ultrafine Aerosols (3 < D p < 10 nm) with Illustrative Data from the Arctic

Four different methods for measuring ultrafine particle size distributions in the 3–10-nm particle diameter range are compared and discussed. These methods all use an ultrafine condensation particle counter (TSI Inc. Model 3025 or its prototype) as the detector, but use different approaches to determine the size of the particles counted. Size classification was achieved using a Hauke Model VIE-06 differential mobility analyzer, a specially configured TSI Model 3040S diffusion battery, an ultrafine condensation particle counter with a variable condenser temperature, and an ultrafine condensation particle counter with a pulse height analyzer for signals produced by the optical detector. The response of these systems to ultrafine particles of known size and composition was studied during a workshop held in Lund, Sweden, during July 1991. After this workshop, measurements of ultrafine particles were made on the Swedish icebreaker Oden during the International Arctic Ocean Expedition 1991 (August 1, 1991 through October 7, 1991). In this article, the results of these laboratory and field measurements are discussed. The strengths and limitations of these measurement methods are emphasized.     

Particle sizing using particle imaging velocimetry for two-phase flows

The major factors influencing the successful measurement of particle size from Particle Imaging Velocimetry (PIV) image data are described. Components of a standard PIV system, a high resolution CCD camera and argon ion laser, are used to capture images of stationary particles. The image data are used to ascertain the limitations of estimating particle size. The effects of the Gaussian distributed intensity variation across the depth of the light sheet and the optical collection system's depth of field are investigated. These effects provide insight into designing a balanced illumination and collection optical system necessary to obtain constant particle size estimates, independent of their position within the light sheet. Using a ‘balanced’ optical set-up, monodisperse particle images are shown to be reproducible and predictable over a range of particle sizes and fields of view. Accuracy in the particle size estimates on the order of 9% are obtained consistently. It is also shown that size distributions in a mixture of polydisperse particles can be obtained with a maximum deviation of 10–20% from the true size distribution.     

Synthesis and characterization of PNIPAM/PS core/shell particles

Crosslinked, monodisperse PNIPAM particles were synthesized by precipitation polymerization. The particle size was measured by dynamic light scattering (DLS), capillary hydrodynamic fractionation (CHDF), and transmission electron microscopy (TEM). Two different polymerization methods were used to prepare PNIPAM/PS core/shell particles, both above and below the volume phase transition temperature (VPPT) using either a semibatch or seeded semibatch polymerization process. In both processes, uniform “raspberry” structures were obtained in which polystyrene formed small domains on the surface of the PNIPAM particles. The resulting core and shell structure was confirmed by temperature‐dependent particle size and density gradient experiments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation of multi-responsive amphiphilic particles by one-step soapless emulsion polymerization

A novel multi-responsive amphiphilic copolymer (mRAP) particles with tunable emulsifiability was successfully prepared via one-step soapless emulsion polymerization using common monomers, such as methyl methacrylate, methacrylic acid (MAA), butyl acrylate (BA) and N,N-diethylacrylamide (DEAA). The obtained monodisperse spherical mRAP particles were characterized by dynamic light scattering, Fourier transform infrared spectroscopy, scanning electron microscope and transmission electron microscope, which provided the information of particle size, components and anisotropic structure. Its multiple responsivities were investigated under the condition of diversified pH values, salinity and temperature. The results showed that the mRAP particles exhibited good dispersivity based on uniform particle size, as well as tunable emulsifiability and anticipated multiple responsiveness. Furthermore, the tunable emulsifiability of oil–water mixtures could be easily achieved by adjusting the mass ratios of MAA to DEAA. Meanwhile, the obtained multi-responsive polymers relying on simple and effective copolymerization can be used in fundamental research and industrial production.     

Simultaneous Use of Polystyrene Latex Particles of Different Sizes to Evaluate Performance of a Cyclone and Impactor

Monodisperse and polydisperse aerosols were produced to evaluate the effect of particle size on cyclone and impactor performance. Monodisperse aerosols were generated from polystyrene latex and divinylbenzene particles. Polystyrene aerosols were also generated by mixing several monodisperse aerosols of different sizes. The mixture ratio of monodisperse aerosols was found by trial and error to generate polydisperse aerosols. Generated polydisperse aerosols had multimodal aerosol size distribution, which had the same peak point as shown in the size distribution of monodisperse particles. The results show the collection efficiency curves of a cyclone and impactor, when generating monodisperse particles were coherent with those for polydisperse ones. Our findings show that the size distribution and the size range of test aerosols can be easily determined by mixing monodisperse particles of known particle sizes, using a time saving procedure.     

Preparation of micron-size monodisperse poly(methyl methacrylate) particles using poly(2-oxazoline) macromonomer

Micron-size monodisperse poly(methyl methacrylate) particles were prepared by dispersion copolymerization of methyl methacrylate with a hydrophilic poly(2-oxazoline) macromonomer in an aqueous methanol solution. The macromonomer acted as a comonomer as well as a stabilizer. As the macromonomer concentration increased, the diameter of the particles decreased. The macromonomer with higher molecular weight, or with more hydrophilic nature, stabilized the particles more effectively The diameter of the particles was dependent on the initiator concentration. Under the conditions giving monodisperse particles, the particle volume increased linearly with the yield of the particles and the particle number was almost constant during the copolymerization. From ESCA analysis of the particle surface, poly(2-oxazoline) chains were enriched on the surface.     

In‐Line Monitoring of Crystallization Processes Using a Laser Reflection Sensor and a Neural Network Model

Laboratory‐scale experiments were carried out for measuring the chord length distribution of different particle systems using a laser reflection sensor. Samples consisted of monodisperse, polydisperse and bimodal FCC catalyst and PVC particles of different sizes, ranging from about 20 to 500 μm. The particles were dispersed in water, forming suspensions with solid‐phase mass fractions ranging from ca. 0.2 % until ca. 30 %. The experimental results, consisting of the particle number counting per chord length class, were used in fitting a neural network model for estimating the mass concentration of particles in the suspension and the volume‐based size distribution, eliminating the effects of suspension concentration and particle shape. The results indicate the feasibility of using such a model as a software sensor in crystallization processes monitoring.     

Modification of the TSI 3081 differential mobility analyzer to include three monodisperse outlets: Comparison between experimental and theoretical performance

Differential mobility analyzers (DMAs) are widely used to determine the size of aerosol particles, and to probe their size-dependent physicochemical properties when two are employed in tandem. A limitation of tandem DMA (TDMA) systems is their long measuring cycle when the properties of more than one monodisperse population of particles need to be probed. In this work, we propose a simple modification of the classical cylindrical DMA by including three monodisperse-particle outlets in its central electrode (namely, the 3MO-DMA), with the objective of using it as the first DMA in TDMA systems for reducing their measuring cycle. The performance of the 3MO-DMA at different flow conditions was evaluated using laboratory-generated aerosol particles, and compared with theoretical predictions. The theory predicted accurately (i.e., within 3%) the geometric mean diameters of the three distinct populations, as well as the resolutions of the first and the third outlet, under all experimental conditions. For the second outlet, the resolution was 10% to 74% lower than that predicted theoretically depending on the sheath-to-aerosol flow ratio. Nevertheless, the geometric standard deviation of the monodisperse aerosol from all the outlets was less than 1.09, which is sufficient for using the 3MO-DMA designed and tested in this work as a first DMA to produce a monodisperse aerosol flow containing three distinct particle populations in TDMA systems.

Copyright © 2016 American Association for Aerosol Research     

Effects of particle size distribution in a three-dimensional micropolar continuum model of granular media

A particle size distribution is incorporated into a three-dimensional homogenisation scheme, devised on the scale of a particle and its immediate (or first ring) of neighbours. Based on this scheme, micropolar continuum models for polydisperse, dry, and densely packed granular assemblies of spherical particles undergoing quasi-static deformation are developed for various particle size distributions. Three different cases are considered: (1) a monodisperse assembly, (2) a defect particle in an otherwise monodisperse assembly, and (3) an assembly of a given particle size distribution. In Case 1, an additional dependence on particle radius is found in 3D systems, compared with previous 2D constitutive laws. In Case 2, it is found that a small (large) particle in an otherwise monodisperse system increases (decreases) the stress compared to a purely monodisperse assembly, but the couple stress may increase or decrease depending on the relative size of the rolling resistance compared with the tangential stiffness coefficients. On the other hand, if the defect particle is substantially smaller or larger than the monodisperse particle size, the stress and couple stress are always increased. In Case 3, three different distributions are examined, i.e. square, normal and a lognormal distribution. For Cases 2 and 3, both the stress and the couple stress increased with the degree of dispersity, from the lower bound value corresponding to the monodisperse system considered in Case 1. Finally, the paper highlights areas that will need to be addressed to enable the future advancement of micromechanical continuum models.