Molecular weight (M n) and functionality effects on CUP formation and stability

The formation of colloidal unimolecular polymer (CUP) particles from single polymer strands was investigated as a function of molecular weight. The CUP particle size was correlated with the absolute molecular weight and its distribution. The characteristics of the particles were evaluated with respect to viscosity, acid number, size distribution, and stability. The particle size varied from less than 3 nm to above 8 nm representing polymers with molecular weight in the range of 3000–153,000. Lower molecular weight polymers were found to be unstable. Particle size measurements using dynamic light scattering technique indicated a normal distribution which corresponded to the molecular weight distribution of the copolymer. The statistical distribution of the acid groups in the polymer chains played a significant role in the stability of low molecular weight polymers.     

The effect of particle shape on the pressure drop across the dust cake

In order to observe the effect of particle shape of poly-dispersed dusts on filter performance, the pressure drop across the dust cakes of fly ashes from a conventional power plant (PC), fluidized bed combustion (FBC), and paint incinerator (FI) was measured over a metal filter element in the accurate conditions. A fluidized bed column was used to prepare the dust feed stream of uniform particle distribution. The fine particles of FI ash have a tendency to be agglomerated at low transport velocity. The aggregates were broken at high velocity of more than 21 cm/sec. FBC ash composed of jagged type particles and containing high concentration of unburned-carbon showed higher pressure drop than that of PC ash composed mostly of spherical particles. FI ash composed of aggregates of very fine carbon particles presented the highest pressure drop among the fly ashes tested. The shape factors of PC, FBC, and FI ash were estimated as 0.91, 0.76, and 0.65, respectively, by the Ergun equation. The results implied that the irregular particle tends to form a higher pressure drop and to be more compressible than spherical one. This paper is dedicated to Professor Wha Young Lee on the occasion of his retirement from Seoul National University.     

Oxidation reaction in graphite—role of particle characterstics

Diffusion controlled reactions involve square of the particle size as a significant controlling factor and great attention should be given to characterize the particles. Common observations are that imperfections present within pores, cracks, voids, etc., play a critical role in further reactions, leading to anisotropic reaction behaviour.

Two different graphites of different physico-chemical properties and having different particle sizes were studied and it was found that the particles, irrespective of their initial particle characteristics, exhibit the same time period for completion of reaction, and the rate of reaction towards completion is variable with particle characteristics and atmosphere employed.     

Radiative transfer modeling of filter-based measurements of light absorption by particles: Importance of particle size dependent penetration depth

We present new physical models to interpret the response characteristics of filter-based measurements of aerosol light absorption. They were motivated by a recently found particle size dependence of a systematic bias in absorption measurements that cannot be interpreted by any models reported thus far. A theory of particle filtration by fibrous filter is applied to reproduce the penetration depth of particles into a filter matrix, and the light transmissivity of the matrix is calculated by the use of radiative transfer theory for plane-parallel layers. Optical properties of individual layers are calculated from microphysical properties and the number density of filter fibers and deposited particles. The size-dependent systematic bias in absorption measurement is successfully explained by the particle size dependence of penetration depth into a filter matrix. In practice the physical models developed here are useful for selecting operating conditions and filter matrices for instruments with fewer systematic biases.     

气泡驱动液固流化床内二元颗粒的流化行为

采用密度稍重于和稍轻于流体的两种颗粒,研究了气泡驱动液固流化床内二元颗粒的流化行为。通过测量压差和拍摄视频的方法确定了初始流化气速U_in,g、固含率和气含率。重颗粒的U_in,g通过流化床底部的压差变化确定,轻颗粒的U_in,g则通过观察得到。研究表明,在气泡驱动的液固流化床内,重颗粒和轻颗粒的初始流化气速都随藏量的增加而增加,但重颗粒增加幅度更大。完全流化后,重颗粒固含率在轴向上分布不均匀,而轻颗粒则分布较为均匀。在二元颗粒体系内,上部轻颗粒的流化受到下部重颗粒的影响而底部重颗粒的流化不受轻颗粒影响,导致重颗粒U_in,g和固含率分布主要受自身藏量影响,而轻颗粒U_in,g随二元颗粒的总藏量变化。     

利用多重光散射法对纳米TiO2水分散体系稳定性研究

通过多重光散射法研究了纳米TiO2水分散体系稳定性的影响因素。文章探讨了分散剂类型、pH和NaCl质量浓度对水分散体系稳定性的影响规律以及分散剂对纳米TiO2颗粒在水分散液中粒径变化、沉降的微观作用特性。结果表明：纳米TiO2颗粒的粒径在100～200 nm时易相互吸附团聚沉降,分散剂会在纳米TiO2颗粒表面吸附形成双电层,产生更大Zeta电位负值,增强颗粒间的排斥作用,减缓粒径增长和发生沉降的作用,从而提升分散液稳定性;纳米TiO2颗粒的较佳分散条件为：w(六偏磷酸钠)=0.05%,pH=9～10且不加电解质NaCl;多重光散射法与传统的吸光度测试实验所得结果基本相符。     

Wind tunnel study and numerical simulation of dust particle resuspension from indoor surfaces in turbulent flows

Particle resuspension from flooring is an important source of air pollution in the indoor environment. In this work, resuspension of monolayer, polydisperse, irregularly shaped dust particles from various types of floorings was studied via a series of wind tunnel experiments. The range of free-stream velocity needed for resuspension of dust particles was evaluated as a function of particle size and material of particles and surfaces. In addition, a Monte Carlo simulation for predicting the resuspension of dust particles was developed. The resuspension model took into account the effects of particle irregularity, particle surface roughness, and flow characteristics. The dust particle resuspension from different floorings for several particle sizes was evaluated. The model predictions for resuspension fractions were compared with the experimental data and good agreement was observed. The study provided information on the role of airflow velocity on irregular dust particle resuspension from common floorings.     

The effect of environmental temperature upon the physical characteristics of the smoke produced by burning wood and PVC samples

Data are presented which show the effect of elevated environmental temperature upon smoke particle characteristics of wood (Douglas fir) and a rigid PVC, under both flaming and nonflaming combustion in air. The physical data obtainbed include the smoke particle average diameter, the smoke optical densities in red and blue light, and the weight loss of the sample. The average particle dimeter, the smoke optical densities in red and blue light, and the weight loss of the sample. The average particle diameter and optical densities in red and blue light, and the weight loss of the sample. The average particle dimater and optical densities were obtained uwing in in situ optical system which measures forward scattered light at two angles and transmitte light at two wavelengths. Data were taken for vertically mounted samples exposed to a radiant flux of 5 W cm^?2 in environments at a room temperatures, 100°C, 200°C and 300°C. The result indicate that in flaming test higher environmental temperatures general result in greater smoke optical densities and larger smoke particles, while in nonflaming tests higherl temperatures in lower smoke densities and smaller smoke particles, for wood. These results may explain why small-scale test data (room temperature environment) do not often correlate well with full-scale data (often at elevated environmental temperatures).     

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.     

Light stabilization of polymers using opaque pigments

The ultraviolet light screening characteristics of monodisperse and polydisperse opaque spherical pigment particles are examined in the nonreflection limit. The screening capability for polydisperse particle size distributions is most uniquely described in terms of the area-average radius. The light screening is related to the pigment's area-average radius and volume fraction loading. Light intensity as a function of depth is stated for systems containing an opaque pigment and a soluble UV light absorber.     

Measurement of Particle Density During Explosive Particle Dispersal

A gauge based on laser light attenuation has been developed to determine the temporal history of particle number density during the explosive dispersal of inert particles. The optical scheme of the gauge employs narrow band pass and spatial optical filters that protect the optical sensors from ambient light and laser light scattered by particles. The gauge is used in field experiments to measure particle density at two locations in close proximity to spherical metalized explosive charges containing a packed bed of either iron, nickel, or glass particles saturated with nitromethane. The heavy iron particles penetrate the blast wave in the near field, whereas the lighter particles remain behind the blast wave. Comparisons with multiphase calculations indicate that the particle density field inferred from the light intensity signals is consistent with the computations until the point at which the combustion products containing soot arrives at the gauge, blocking the laser light.     

Mathematical model of migration of spherical particles in tube flow under the influence of inertia and particle-particle interaction

In this paper, a mathematical model is considered of the migration of non-colloidal, spherical particles suspended in Newtonian fluid under Poiseuille flows by combining the inertial migration theory by Ho and Leal (JFM, 1974) and particle migration model in concentrated suspension by Phillips et al. (Phys. Fluids, 1992). The numerical solutions of the model equations reveal that the model set up here explains the experimental observation reported in the literature when Re_p>1, at least qualitatively. It was concluded that both the inertia and particle-particle interaction should be taken into account properly to understand the particle migration in tube flow of suspension regardless of particle loading. This paper is dedicated to Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University.     

颗粒形状对全散射法测量颗粒物质量浓度的影响

燃煤电厂排放颗粒物作为大气颗粒物主要来源之一受到广泛关注,实现颗粒物质量浓度的精确在线监测意义重大。激光全散射法作为一种常用的颗粒物质量浓度在线监测方法,受颗粒特性影响较大,易造成较大的测量偏差。为探究颗粒形状对全散射法测量的影响,搭建了全散射法测试台架,并采用球形二氧化硅颗粒对测试系统进行标定,标定结果显示,球形二氧化硅颗粒质量浓度与消光程度高度线性相关,相关系数R2>0.99,测量浓度与真实浓度偏差仅为1.8%。进一步采用633 nm与532 nm波长激光分别对3种非球形(棱形、不规则和片状)二氧化硅颗粒进行测试试验。测试结果显示,3种形状颗粒物的质量浓度与消光程度均高度相关,R2均高于0.99;3种形状颗粒物质量浓度的测量值与真实值偏差与颗粒形状及激光波长相关,对比发现,入射波长为633 nm时,不规则、棱形和片状颗粒的质量浓度测量值与真实值的测量偏差分别为16.1%、27.4%和36.6%;入射波长为532nm时,3种颗粒质量浓度的测量偏差分别为4.8%、11.4%和17.4%;颗粒形状一致条件下,532 nm入射波长时的测量偏差明显较小,通过波长的选择可降低颗粒形状变化造成的测量偏差。     

Stability of particle suspensions after fine grinding

The objective of this work was to investigate the physical stability of sub-micron particle suspensions of organic crystalline food compounds after grinding. A Dynomill ball mill was used in combination with zirconium oxide grinding medium beads. The organic product was a poor water soluble product. During grinding the average particle diameter of the particulate product was reduced to a minimum value in the sub-micron range. Forward light scattering was used to analyze the particle size distribution. Dynamic light scattering measurements, on the other hand, showed that there were aggregates present after grinding. The difference in the obtained particle size distributions using both techniques was related to the shear in the measurement device, i.e. in the laser diffraction measurement the shear was higher than in the dynamic light scattering device. Thus in the laser diffraction measurement the aggregates were broken up by shear, while this was not the case in the dynamic light scattering measurements. The difference in the measurements showed that the particles formed aggregates at low to zero shear.The aggregation behaviour of the particles was studied by measuring the sedimentation behaviour of the particles suspension at various pH values. The impact of the pH on the aggregation rate was explained by the zeta potential of the particles. The suspensions were less stable near the iso-electric point of the particles.     

Molecular dynamics studies of two hard-disk particles in a rectangular box I. Thermodynamic properties and position autocorrelation functions

Molecular dynamics simulations have been carried out for the simple few-body systems of two hard-disk particles confined within a 2-dimensional rectangular box. Wall pressures, the collision frequencies, density profiles, two-particle probability distributions, and position autocorrelation functions were computed to examine the thermodynamic, structural and time-dependent properties of such systems. Excellent agreement was found between simulation results and theoretical predictions recently proposed by Munakata and Hu. Detailed dynamic effects are also discussed to describe configurational particle trajectories including fast/slow relaxation processes observed in the position autocorrelation functions. Professor Hyun-Ku Rhee on the occasion of his retirement from Seoul National University     

纳米SiO2复合粒子/有机硅低聚物透明超疏水复合涂层的制备及其性能

本文以Stober法制备的胶体SiO2粒子与粉体SiO2粒子结合的SiO2复合粒子在玻璃基底构建粗糙表面,以三乙氧基甲基硅烷（MTES）与正硅酸乙酯（TEOS）为前聚体制备的酸性有机硅低聚物作为粘接剂,使用偶联剂KH540与氟硅烷PFDT进行改性,通过喷涂法在玻璃基底上制备出SiO2复合粒子/酸性有机硅低聚物复合透明超疏水涂层,然后探究SiO2复合粒子、酸性有机硅低聚物、偶联剂KH540以及氟硅烷PFDT对复合涂层的影响。研究表明：当SiO2复合粒子由粒径为110 nm的胶体SiO2粒子与粒径为50 nm的粉体SiO2粒子两种粒子组成,SiO2复合粒子溶液与酸性有机硅稀释液的混合质量比为4:1,添加偶联剂KH540与氟硅烷PFDT的质量比为混合液的1%时,复合涂层在可见光波长范围内透光率可达88%,静态接触角能达155°,在800目砂纸上磨损60 cm后仍能保持超疏水性能,具有良好的自清洁性,为透明超疏水涂层的制备提供一种简便、低成本方案。     

振荡流态化现象及应用

研究了轻颗粒振荡流态化现象,通过对颗粒在振荡体中运动方程的求解,得到了单颗粒运动模型及重颗粒克服重力漂浮或者轻颗粒逆浮力下沉的临界参数关系式.用五种粒径、三种不同密度的轻颗粒实验数据及梁百申、邓勇有关重颗粒的数据验证了模型,结果表明实验值与理论值吻合较好.同时,从理论上得到流体在振荡情况下颗粒床层松散的数学表达式,并以实验进行了验证.振荡流态化反应器用于固定化细胞发酵酒精,可解决发酵过程产生的CO_2气体附着在酵母载体表面导致发酵过程操作条件恶化的问题,提高了操作稳定性和发酵反应速度.     

Light Scattering Instrumentation for Aerosol Studies: An Historical Overview

ABSTRACT

The most powerful and elegant method for determining particle size distributions of aerosols by light scattering is to observe single particles suspended in a Millikan–Fletcher electrostatic field. The first such light scattering studies were carried out by Whytlaw-Gray and Patterson (1926), by Gucker and Egan (1961), and then by Wyatt and Phillips (1972). Optically levitated particles were studied by Grehan and Gousebet (1986). Optical particle counters were devised by Gucker and his associates (1947a,b) and Gucker and Rose (1954) for both forward and 90° viewing. Gucker also built an instrument for on-line viewing of 360° scatter by particles flowing through a light beam in single file. Individual particles were also analyzed in an ultramicroscope by Wells and Gerke (1919). The earliest angular scattering patterns from assemblies of particles were by Tolman and Vliet (1921) and by Sinclair and La Mer (1949). Other interesting systems have utilized acoustic detectors, power loss in a laser cavity, and Doppler shifted light scattering signals.     

TiC颗粒弥散Al2O3复合材料的阻力曲线行为

研究了ＴｉＣ颗粒弥散ＡＩ２Ｏ３复合材料的阻力曲线行为,发现ＴｉＣ颗粒对ＡＩ２Ｏ３基体的增韧效果在很大程度上取决于ＴｉＣ颗粒的尺寸,在ＴｉＣ颗凿尺寸较小的情况下,复３事材料的断裂韧性与ＡＩ２Ｏ３着ＴｉＣ颗粒尺寸的增大而增大,本工作 地裂纹扩展途径的观察,简要讨论了ＴｉＣ颗粒弥散ＡＩ２Ｏ３复合材料中的增韧机制。     

Characterization of particle contamination in process steps during plasma-enhanced chemical vapor deposition operation

The occurrence time and the contribution level of particle contamination on the wafer in individual steps during plasma-enhanced chemical vapor deposition (PECVD) operation were investigated. A method was proposed to determine the occurrence time of particle contamination by making use of the capability of thermophoresis to shield the wafer from particle deposition. The level of particle contamination on the wafer was determined by a scanning electron microscopy (SEM) and the particle behavior in the reactor was observed using a laser light scattering (LLS) technique. The particles were continuously injected into the plasma reactor from the outside. Using this technique, the effect of particle size on the particle behavior can be studied with high certainty. It was found that the particle contamination occurred during the postplasma when the injected particles were trapped in the sheath region below the powered electrode. On the other hand, when the injected particles were not trapped due to a strong inertial effect of particle, the contamination occurred during plasma operation. There is a regime of operation condition in which the lowest level of contamination occurs. Most particles retained their negative charge in the postplasma as shown by their movement and deposition on the wafer in the presence of either a negative or positive dc field. The charge on these particles was determined from particle motion with high certainty using the current experimental technique.