Resolving Concentrated Particle Size Mixtures Using Dynamic Light Scattering

Dynamic light scattering (DLS) is a technique used for measuring the size of molecules and particles undergoing Brownian motion by observing time‐dependent fluctuations in the intensity of scattered light. The measurement of samples using conventional DLS instrumentation is limited to low concentrations due to the onset of a phenomenon called multiple scattering. The problems of multiple scattering have been addressed in a light scattering instrument incorporating non‐ invasive backscatter optics (NIBS). This novel optic arrangement maximizes the detection of scattered light while maintaining signal quality and allows for measurements of turbid samples. This paper discusses the ability of backscatter detection to accurately determine particle sizes at 1 %w/v sample concentrations and demonstrates the correct resolution of different size populations using a series of latex standard mixtures with known volume ratios. The concentration of 1 %w/v is much higher than can be measured on conventional dynamic light scattering instruments.     

双峰分布颗粒体系的多角度动态光散射数据反演

采用多角度动态光散射和加权正则化反演方法,对4组模拟的双峰分布颗粒体系(100/600 nm,200/600 nm,300/600 nm和350/600 nm)分别选取1、3、6和10个散射角进行测量.粒度反演结果表明,采用加权正则化方法反演双峰颗粒体系的多角度动态光散射测量数据,可获得峰值位置比小于2∶1且含有大粒径(＞350 nm)颗粒的双峰颗粒粒度分布.采用标准聚苯乙烯乳胶颗粒进行实测的结果验证了这一结论.得到含大粒径颗粒的双峰粒度分布反演结果的原因在于,多角度动态光散射能提供更多的大粒径颗粒的粒度信息,加权正则化反演方法能减少测量数据中的噪声,因而多角度动态光散射测量数据的加权反演能实现峰值位置比小于2∶1且含有大粒径颗粒的双峰颗粒体系的测量.     

应用低相干动态光散射法测量悬浮液中的颗粒粒径分布

利用低相干动态光散射法测量不同浓度悬浮液中的颗粒粒径分布。由低相干光源和迈克尔逊干涉仪,结合传统的动态光散射技术组成低相干动态光散射装置,通过检测单次背散射光的能谱分布,利用CONTIN算法得到不同浓度悬浮液中颗粒的粒径分布。结果表明,对于1%～10%体积浓度范围内的单分散悬浮液羊品测量得到的颗粒粒径精确度在4%以内。     

动态光散射测量粒径分布的格雷码编码遗传算法反演运算

采用格雷码编码的遗传算法对动态光散射测量的粒径分布进行反演运算,数字测试结果表明,对于无噪声的分布,算法能精确的反演出各种粒子分布图像;对于加了一定噪声的分布,算法显示出较好的稳定性,能反演出主峰的分布图像.聚苯乙烯乳球的实验结果表明,该算法能反演双分布的粒径分布图像.与标准遗传算法和反演蒙特卡罗算法相比,该算法具有较高的搜索效率,能够用较少的计算时间快速搜索到最优解.格雷码编码遗传算法是一种更有效的随机反演算法.     

颗粒溶液颗粒尺寸及浓度的差分偏振弹性散射光谱在线分析方法

偏振弹性散射光谱技术的基本原理为在偏振光入射条件下,根据出射光的偏振特性不同可以筛选出浅表层组织的单次散射光信息和深层组织的漫散射光信息。该研究的创新点在于将这种方法应用于颗粒溶液检测,目的是在颗粒溶液原始状态下实现对颗粒尺寸及浓度的同时检测。设计了一个共轴笼式光学系统,测量了聚苯乙烯微球颗粒溶液某一角度的背向散射信号,通过控制入射端和收集端偏振片的偏振方向获得了颗粒溶液的偏振平行光谱与偏振垂直光谱,两者之差即偏振差分光谱对应颗粒的单次散射信息,将该单次散射信息与Mie散射数据库进行比对获得颗粒的尺寸,然后在颗粒尺寸作为已知的条件下进一步分析偏振垂直光谱,将该垂直光谱对应的颗粒溶液的漫散射信息代入光漫散射下的近似表达式拟合得到颗粒的浓度信息。将实验结果与样品提供值进行了比对,并进一步分析了在获取颗粒数浓度时,颗粒直径的方差分布对结果的影响,最终验证了该实验方法的可行性。该方法的潜在应用包括对标准颗粒制造厂商的产品在线检测以及对牛奶制品中脂肪和蛋白质的浓度检测研究。     

利用低相干光纤动态光散射法测量浓悬浮液中多分散颗粒粒径分布

本文针对高浓度散射介质,用低相干光纤动态光散射技术测量浓悬浮液中多分散颗粒系的粒径及其粒径分布。利用迭代CONTIN算法对实验数据进行反演运算,得到多分散颗粒系的粒径分布结果。结果表明,浓悬浮液中多分散颗粒系的峰值粒径测量值与给定的两种标准粒径值相吻合,其误差在4%之内,粒径分布曲线中各散射颗粒所反映的散射体光强分布与根据Mie散射计算得到的理论值相吻合。实验结果证明低相干光纤动态光散射实验系统能准确测量浓悬浮液中多分散颗粒粒径及粒径分布。     

Determination of Soot Particle Size in a Premixed Flame: a Static and Dynamic Light Scattering Study

In this contribution we report upon our static and dynamic light scattering experiments to characterize soot particles in flames. We studied sooting laminar premixed flame with acetylene as fuel mixed with air as oxidizer. The air equivalence ratio of the combustion was larger than one. We used a Kaskan type burner with circular geometry and a stabilizing flow of nitrogen around the flame. We focused on the determination of the size of the soot particles in the center of the flame as a function of height above burner. In addition we investigated the influence of the mixing ratio of the gases on the size of the particles. Our results show that static light scattering is better suited than dynamic light scattering for a fast and reliable characterization of soot particles in flames. The latter needs detailed a priori information about the flame to allow the unique determination of sizes from the diffusion measurements. The soot particles grow monotonously with height above burner and with decreasing air equivalence ratio. The aggregates have a fractal dimension lower than two.     

CS-QT-TPP纳米颗粒的动态光散射分析

本文利用CS与TPP的交联作用包覆QT制备CS-QT-TPP纳米颗粒,并以动态光散射研究QT浓度、CS分子量及CS/TPP重量比对所得纳米颗粒粒径与Zeta电位的影响。结果表明,QT浓度由0.15mg/mL升至0.45mg/mL时粒径增大,而继续升至0.75mg/mL时粒径稍微减小;CS分子量越高,粒径越小;而CS/TPP重量比对粒径则无明显影响。CS-QT-TPP纳米颗粒粒径介于711~759nm之间。CS分子量较低时表面电位较小,而QT浓度与CS/TPP重量比则对Zeta电位无明显影响,CS-QT-TPP纳米颗粒表面均带正电,介于25.7~39.8mV之间。因此,QT浓度为0.75mg/mL、CS高分子量为380kDa及CS/TPP重量比为3/1时制备CS-QT-TPP纳米颗粒最佳。     

激光散射法对尿液中纳米微晶粒径及其分布的研究

泌尿系结石已经成为威胁人类健康的一种常见病、多发病,目前对其形成的机制尚不清楚。文章采用激光散射法测定了正常人尿液和尿石症患者尿液中纳米粒子的粒径和粒径分布,该方法快速准确、经济、容易操作。正常人尿液比尿石症患者尿液的稳定性好,归因于正常人尿液中纳米微晶尺寸分布均匀,不容易聚集,而尿石症患者尿液的纳米微晶尺寸分布不均匀,粒子间容易聚集而沉降。通过分析尿样稀释、离心或者用微孔滤膜过滤后体系的光强-自相关函数曲线,得到了制备稳定的尿样悬浮液的方法：尿样先稀释20%,然后离心或用1.2 μm微孔滤膜过滤,可得到稳定的尿液悬浮液。激光散射法结果与TEM检测结果一致。从尿液中存在的范德华力、尿液粘度、酸碱性、离子强度、尿液中纳米微晶的表面电荷和Zeta电位等方面解释了尿液稳定的原因。     

Particle Size Distributions from Static Light Scattering with Regularized Non‐Negative Least Squares Constraints

Simulated data from static light scattering produced by several particle size distributions (PSD) of spherical particles in dilute solution is analyzed with a regularized non‐negative least squares method (r‐NNLS). Strong fluctuations in broad PSD's obtained from direct application of NNLS are supressed through an averaging procedure, as introduced long ago in the inversion problem in dynamic light scattering. A positive correlation between the best PSD obtained from several averaging schemes and the condition number of the respective data transfer matrices was obtained. The performance of the method is found to be similar to that of constrained regularization (CONTIN), which uses also NNLS as a starting solution, but incorporates another regularizing strategy.     

可见-红外波段光全散射法颗粒粒径测量范围的研究

在光全散射法颗粒粒径测量中,采用独立模式算法在可见-红外波段对粒径测量范围进行了深入的研究。通过对多种R-R分布函数反演结果进行分析,比较,以确定光全散射法颗粒粒径测量范围。同时在消光系数计算中,采用修正的消光系数代替原始的消光系数,以便得到更准确的粒径测量范围。仿真计算结果表明,在可见-红外光谱区,相对折射率m=1.235时的粒径测量范围为0.05～18 μm。在此区域内测量粒径分布,反演结果与真值基本吻合。随着颗粒相对折射率、波长范围的变化,粒径测量范围也随之发生改变。采用限制最小二乘算法能够最大限度地克服随机噪声对测量结果的影响,使测量的精度和可靠性明显提高。对测量的消光值加入±1%随机噪声时,颗粒粒径分布的反演均能得到满意的结果。     

Global Analysis of Dynamic Light Scattering Autocorrelation Functions

Dynamic light scattering has become a standard technique of investigating colloidal suspensions and polymer solutions. The experimental field autocorrelation function ĝ₁ (t) can often be well modelled by a Laplace transform relating ĝ₁ (t) to a distribution of decay times A(τ). In simple systems A(τ) can usually be directly related to a distribution of molecular weights, particle sizes, diffusion coefficients or other physically relevant quantities, With constrained regularization methods, the parameter-free estimation of A(τ) has become straightforward. In complex systems, the resulting A(τ) may contain several components the identification of which is not always obvious. The problem often originates in a superposition of diffusive and angle-independent components that have different variations of their respective decay times with the scattering vector. A method is presented based on a simultaneous fit of several autocorrelation functions measured at several different scattering angles, which, using simple and reasonable assumptions, yields a robust analysis of the spectra of decay times. The application of the method is illustrated on simulated autocorrelation functions and also on real experimental data obtained on a variety of different polymer systems.     

Particle Size Distribution Retrieval from Elastic Light Scattering Measurements by a Modified Regularization Method

Retrieval of polymeric emulsions Particle Size Distribution (PSD) from Elastic Light Scattering (ELS) measurements requires the solution of an ill conditioned inverse problem. In this paper we compare the performance of classical regularization methods such as Truncated Singular Value Decomposition and Tikhonov's, to a regularization technique due to Pike that includes positivity constraints on the PSD. We also propose a new method that combines Tikhonov's approach with Pike's method. Simulated ELS measurements for two polymeric materials were generated under different experimental noise assumptions. Uncertainties on the polymer refractive index value were also considered. The PSD estimations obtained show that the implementation of the proposed more sophisticated algorithm is convenient for this very ill‐conditioned problem.     

Fire Smoke Particle Size Measurement Based on the Multiwavelength and Multiangle Light Scattering Method

A multiwavelength and multiangle mathematical model （MWMA） is developed, and the corresponding influence factors of the model are analysed by the numerical calculation, Combined with measurement data of radiation flux and the curve in theoretical calculation, particle sizes of different materials can be obtained, it is found that smoke particle size gradually decreases from land plaster, cotton wick, beech wood, polyurethane, sandalwood, decahydronaphthalene, to N-heptane,     

A Novel Device for Single Particle Light Scattering Size Analysis and Concentration Measurement at High Pressures and Temperatures

Based on the findings of previous work, a novel instrument was developed for the size analysis and concentration measurement of particles dispersed in gases at high temperatures (600 °C) and pressures (16 bar). The main motivation for the construction of this device was a measurement requirement at the conditions of a pressurized pulverized coal combustion (PPCC) test installation in Dorsten, Germany. The development of a high efficiency (> 50 %), coal based, combined cycle process, and specifically, the development of efficient gas cleaning technology for gas combustion under demanding conditions (1400 °C and 16 bar) was the main target. A suitable measurement technique was required for the determination of particle size and concentration downstream of the gas cleaning equipment, which is able to operate close to the given conditions. The performance of the novel device was tested in several measurement series with various monodisperse aerosols at ambient conditions as well as in high pressure, high temperature situations with very satisfactory results, i.e., the lower detection limit (50 % counting efficiency at ca. 0.3 μm) and resolution of the novel device are comparable to state of the art instruments (of the same principle) intended for room temperature operation.     

Particle Sizing by Dynamic Light Scattering: Noise and distortion in correlation data

Two undesirable effects occur in particle sizing by dynamic light scattering; statistical noise, and distortion of correlation data. Statistical noise in the correlation data, caused by estimating the autocorrelation of scattered laser light by a time average, leads to non-physical artifacts in the resulting linewidth distribution. These may be removed by regularization, computer modeling, or other techniques. The regularized kernel function for inverting the Laplace transform is calculated, and used to illustrate the problem of noise. Correct choice of the regularization parameter gives the minimum overall error. It is found that excessive error occurs unless the linewidth distribution is modeled over a finite range. Analytical models for the linewidth with finite range, based on the beta distribution of probability theory, are given. Distortion of correlation data may occur in three ways, through a focused or otherwise nonuniform laser beam in the optical system, by insufficient bit resolution in the quantized detection of scattered laser light, or by calculating a first order field autocorrelation from a second order intensity autocorrelation. Unlike noise, distortion cannot be removed by any known methods, since the exact nature of the distortion is unknown. Several examples illustrate how distortion can lead to artifacts in the linewidth distribution which could easily be misinterpreted as segments of a size distribution, not present in the physical sample.     

Modeling of Multiple Scattering Effects in Fraunhofer Diffraction Particle Size Analysis

A model for the direct problem of calculating the forward scattering signature of a multiple scattering medium is presented. The new formulation is optimized for integration into schemes for reconstructing the particle size distribution from laser diffraction (forward scattering) signatures obtained from optically thick media. The analysis is valid for media where the particle sizes and interparticle spacings are large (relative to the wavelength and the particle size, respectively) such that Fraunhofer diffraction theory adequately describes the properties of the forward scattered light from individual scattering events. The simulated performance of laser diffraction particle sizing instruments was then studied using predictions of the scattered light signatures which would be measured by laser diffraction instrument under multiple scattering conditions. The results were compared with experimental data and theoretical calculations based on other models.     

动态光散射中的多普勒效应

动态光散射中的多普勒效应郭凤岐１）刘秋霞２）（武汉工业大学数理系材料学院武汉４３００７０）ＤｏｐｐｌｅｒＥｆｅｃｔｉｎＤｙｎａｍｉｃＬｉｇｈｔＳｃａｔｅｒｉｎｇＧｕｏＦｅｎｇｑｉ，ＬｉｕＱｉｕｘｉａ（Ｄｅｐｔ．ｏｆＭａｔｈ．ａｎｄＰｈｙｓ．，Ｗｕｈａ...     

动态光散射技术的角度依赖性

与单角度动态光散射技术相比,多角度动态光散射(MDLS)颗粒测量技术能够提高颗粒粒度分布的测量准确性。但在MDLS技术中,测量角度的选择常常与被测颗粒体系的分布有关。对100nm、500nm的单峰模拟分布和300nm与600nm混合的双峰模拟分布的颗粒体系,分别在1、3、6、9个散射角条件下进行了测量。颗粒粒度反演结果表明,随着散射角个数的增大,颗粒粒度分布更趋于真实的颗粒粒度分布。对数量比为5:1的100nm与503nm双峰分布的聚苯乙烯颗粒,分别在1、3、5、10个散射角条件下进行了测量,实测结果表明采用单角度测量只能得到单峰分布,3个及更多散射角可得到双峰分布,并且双峰的数量比随散射角数量的增加逐渐趋近真实的数量比。因此,MDLS颗粒测量技术能够改善颗粒粒度分布的测量结果,但这种改善程度会随散射角的增多逐渐降低。由于散射角个数的增多会增加散射角的校准噪声和光强相关函数的测量噪声,因而会导致在有些情况下颗粒粒度分布的测量结果反而变差。     

小粒子动态光散射信号的计算机模拟及分析

用计算机模拟了小粒子（０．００１μｍ～１μｍ）的动态光散射信号，并对其进行了分析，同时运用分形几何学（ＦｒａｃｔａｌＧｅｏｍｅｔｒｙ）的理论和概念，对信号的时间复杂性进行了分数维（ＦｒａｃｔａｌＤｉｍｅｎｓｉｏｎ）的计算，得出了它与粒子尺寸之间的关系。