Calibration of Polarization-Sensitive and Dual-Angle Laser Light Scattering Methods Using Standard Latex Particles

A polarization-sensitive laser light scattering (PSLLS) method and a dual-angle laser light scattering (DALLS) method have been studied for in situ measurement of submicrometer hydrosol and aerosol particles. By using standard monodisperse polystyrene latex particles suspended in water and air as test particles, calibration of systems built based on the above methods have been performed. The effects of light scattered by agglomerated aerosol particles (multiplets) were corrected by considering the fraction of multiplets as determined with an aerosol measurement technique using a differential mobility analyzer. The change in the measured intensities of scattered light with particle diameter was then determined by calculations based on Mie theory. It was shown that the PSLLS system can determine particle diameters as small as approximately 60 nm for the test hydrosol particles and approximately 100 nm for test aerosol particles, respectively. The DALLS system can determine smaller diameters than the PSLLS system for test particles with no light absorption. The change in scattered light intensities with particle diameter was also investigated by theoretical calculations with various refractive indexes and scattering angles. The PSLLS and DALLS systems promise to become routine measurement tools for absorbing and nonabsorbing particles, respectively. Copyright 2001 Academic Press.     

Size distribution analysis of polymer latex systems by use of the extrema in the angular light scattering pattern. III. Unpolarized and horizontally polarized scattered light

The extrema in the unpolarized and the horizontally polarized angular scattering patterns are used as a basis for size-distribution analysis of polymer latex systems composed of single, spherical, optically isotropic particles. The method of analysis is similar to that recently proposed for vertically polarized scattered light and the polarization ratio, where the modal diameter and a distribution width parameter are determined from the experimental angular scattering pattern and prepared theoretical diagrams obtained by Mie theory calculations. The method of analysis, based on all four scattering functions, is illustrated by use of a Dow polystyrene latex sample.     

Small-angle polarized light scattering from amorphous spheres

Small-angle light-scattering measurements have been made using micron-diameter isotropic and spherical polymer latex particles placed between crossed polarizers. Four-leaf clover patterns are obtained, reminiscent of those commonly found for spherical birefringent scatterers. The experimental results compare closely with predictions of Mie scattering theory for isotropic spheres.     

Separation and detection of individual submicron particles by capillary electrophoresis with laser-light-scattering detection

Separation and detection of individual submicron polystyrene spheres using capillary electrophoresis with laser-light-scattering detection has been demonstrated. Electrophoretically separated particles were passed through a focused laser beam and light scattered from individual particles was collected at 90 degrees. Each diameter of polystyrene spheres injected (from 110 to 992 nm) resulted in the observation of a well-defined migration window containing multiple peaks, each arising from the light scattered by an individual particle. The migration time window for individual particles of a particular size corresponded well to the migration time of a peak from a population of particles of the same size detected using a UV absorbance detector. The electrophoretic mobility and scattered light intensity were determined for each particle detected. The average scattered light intensity for each particle size was consistent with Mie scattering theory. Particles as small as 110 nm in diameter were detected individually using this method, but particles with a diameter of 57 nm could not be individually detected. The number of single particle scattering events was counted and compared to the theoretical number of particles injected electrokinetically, and the detection efficiency determined ranged from 38 to 57% for polystyrene spheres of different sizes. The laser-light-scattering detection method was directly compared to laser-induced fluorescence detection using fluorescent polystyrene microspheres. The number of particles detected individually by each method was in agreement.     

Polymerization of acrylamide and methylmethacrylate at the surface of submicron polypyrrole particles

This paper presents two methods of encapsulation of polypyrrole latex particles of different sizes by an insulating polymer. The first method concerns the encapsulation by inverse emulsion polymerization of acrylamide with crosslinking agent. That method is effective for the smallest particles (about 100 nm). The second method concerns encapsulation by direct emulsion polymerization of methylmethacrylate. Inhibition of polymerization occurs if potassium persulfate is used as the initiator, whereas no inhibition is observed with 4,4′ azobis 4-cyanopentanoic acid as the initiator. These results are explained in terms of the ion-exchange capacity of conducting polymers. This second method seems to be effective for all the sizes of polypyrrole particles. These encapsulated particles have been characterized by transmission electron microscopy, scanning electron microscopy, quasi elastic light scattering, cyclic voltametry and electrophoresis. Cyclic voltammetry recently developed on aqueous suspensions of polypyrrole particles was revealed to be the best technique because of its simplicity and speed.     

Preparation of HPMC–EA–DMAEMA nanosized latex

Nanosized copolymer latex of hydroxypropylmethylcellulose (HPMC) grafted with ethyl acrylate (EA) and dimethylaminoethyl methacrylate (DMAEMA) has been prepared by acidifying submicron-sized latex particles synthesized by soap-free emulsion graft copolymerization using potassium persulfate (KPS) as initiator. The effects on the diameter of the latex particles of different conditions, for example concentration of DMAEMA, amount of HPMC, and ratio of HCl to DMAEMA for acidification, were investigated. It was found that increasing the mole ratio of HCl to DMAEMA to 1.0 and increasing the DMAEMA content both resulted in a decrease in particle diameter, whereas increasing the amount of HPMC resulted in larger particle sizes. Measurement by dynamic light scattering (DLS) revealed the diameter of the latex particles was >200 nm before acidification and <100 nm after acidification. Evidence of grafting was obtained by use of Fourier transform infrared (FTIR) spectroscopy. Transmission electron microscopy (TEM) was used to characterize the morphology of the copolymer particles before and after acidification.     

Cavity ring-down spectroscopy measurements of single aerosol particle extinction. I. The effect of position of a particle within the laser beam on extinction

A continuous wave distributed feedback diode laser operating in the near infrared at wavelengths close to 1650 nm has been used to measure the extinction of light by single aerosol particles. The technique of optical feedback cavity ring-down spectroscopy (CRDS) was used for measurement of CRDS events at a repetition rate of 1.25 kHz. This very high repetition rate enabled multiple measurements of the extinction of light by single aerosol particles for the first time and demonstrated the dependence of light scattering on the position of a particle within the laser beam. A model is proposed to explain quantitatively this phenomenon. The minimum detectable dimensionless extinction coefficient epsilonmin was determined to be 3x10(-6). Extinction values obtained for single spherical polymer beads from a monodisperse sample of particles of diameter of 4 microm are in near-quantitative agreement with the values calculated by the Mie scattering theory. The deviations from the Mie theory expected for measurement of extinction by CRDS using a continuous wave laser are discussed in the companion paper.     

Size distribution analysis of polymer latex systems by use of extrema in the angular scattering intensity

The angular position of the extrema of the vertically polarized scattering intensity has previously been utilized for a method of particle size analysis for systems of monodisperse, spherical, isotropic particles which conform to the Rayleigh-Gans-Debye theory. The consequences of a finite polydispersity, which is always present in real systems, was not assessed and the application of the method has resulted in erroneous characterization of some latex systems. This work is concerned with (1) reporting the effects of finite polydispersity on the method of analysis, (2) pointing out previous misuse of the method, and (3) introducing a method of analysis which is based on the position of the extrema but which also considers polydispersity and the exact Mie calculation. This method enables one to characterize a scattering system in terms of a modal diameter and a distribution-width parameter by utilizing prepared diagrams for a particular relative refractive index.     

Angle‐dependent light scattering by highly uniform colloidal rod‐shaped microparticles: Experiment and simulation

While extensive theoretical work has been devoted to analyzing scattering behavior for nonspherical particles, few experimental studies of the light‐scattering properties of such particles are available, largely because of the difficulty of synthesizing such particles with uniform geometries. Here we report the synthesis of highly uniform, volume‐equivalent rod‐shaped colloidal particles prepared from their commercial spherical counterparts, on which we performed light scattering experiments as a function of scattering angle for micro rods with varying aspect ratio and volume. These results were compared to values calculated using the T‐Matrix method. Good agreement with theoretical predictions was found for the experimentally measured scattering cross sections and the angular dependence of the scattering intensity. An increase in the forward scattering intensity is observed and predicted for particles with larger aspect ratios relative to their volume equivalent spheres, with only minor differences observed at both mid‐range and backscattering angles. Furthermore, the light scattering results for the rod‐shaped particles did not show the scattering fringes seen in scattering by the spheres, indicating that as three‐dimensional symmetry is broken, the associated Lorenz–Mie resonances are strongly attenuated. This observation also was predicted by theory. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016 , 54, 1889–1895     

Sedimentation measurements with the analytical ultracentrifuge with absorption optics: influence of Mie scattering and absorption of the particles

Analytical ultracentrifugation is one of the most powerful methods for the characterization of nanoparticles since the days of its invention due to its high resolution and statistical significance. Latexes with different sizes and their mixtures have been measured by sedimentation with the analytical ultracentrifuge (AUC) OPTIMA XL-I (Beckman Coulter, Palo Alto, CA, USA) with interference optics at λ ₀ = 675 nm and absorption optics at λ ₀ = 546 and 263 nm. Additionally, a blue pigment with high absorption characteristic at visible light has been investigated. A large influence of Mie scattering and Mie absorption on the particle size distribution with respect to absorption optics and samples with moderate or broad size distribution is observed. Therefore, the consideration of the Mie scattering effect is compulsory for most AUC measurements of nanoparticles with absorption optics.     

Constructing Mie‐Scattering Porous Interface‐Fused Perovskite Films to Synergistically Boost Light Harvesting and Carrier Transport

Light harvesting (LH) and carrier transport abilities of a photoactive layer, which are both crucial for optoelectronic devices such as solar cells and photodetectors (PDs), are typically hard to be synergistically improved. Taking perovskite as an example, a freeze‐drying recrystallization method is used to construct porous films with improvements of both LH and carrier transport ability. During the freeze‐drying casting process, the rapid solvent evaporation produces massive pores, the sizes of which can be adjusted to exploit the Mie scattering for enhancement of the LH ability. Meanwhile, owing to the strong iconicity, the interface between perovskite nanocrystals fused during recrystallization, which favors carrier transport. Subsequently, PDs based on these Mie porous and interface‐fused films show a high on/off ratio of more than 10⁴ and an external quantum efficiency value of 658 % under 9 V bias and 520 nm light irradiation.     

Particle size measurements of heterogeneous film-forming latexes

Two-phase latex particles consisting of mainly polystyrene (PS) and polyisoprene (PI) in ratios varying from 7030 to 2080 were prepared using different polymerization techniques. Methacrylic acid (MAA) was used in small amounts as a comonomer. The latexes had narrow size distributions, and showed different particle morphologies depending on the monomer composition and the polymerization conditions used. In most cases the latexes were filmforming at room temperature. Particle size distributions and average particle sizes of the latexes have been determined using different particle sizing methods.Size determination by TEM was performed after staining with osmium tetroxide (OsO₄) or uranyl acetate (UAc). The staining methods showed no significant differences in particle size averages and particle size distributions when the ratio between the PI and PS phase did not exceed 5050. At higher phase ratios OsO₄ staining was preferred. The glass transition temperature of the PI phase increased after OsO₄ staining, which prevented deformation of the latex particles. Particle morphologies for the heterogeneous latex particles were also determined after OsO₄ staining.Particle sizes measured by TEM were generally smaller than the corresponding sizes measured by quasielastic light scattering (QELS). The difference in the measured diameters increased with increasing PI and PMAA content in the latex particles. The larger sizes observed by QELS are results of the presence of an immobilized water layer surrounding the particles in the aqueous environment, water absorption and swelling due to the presence of carboxylic acid groups, and adsorption of soluble carboxylated polymers forming a hydrophilic corona around the particles. By TEM the hard sphere diameters of dehydrated particles are measured.     

Micro-impedance cytometry for detection and analysis of micron-sized particles and bacteria

The sensitivity of a microfluidic impedance flow cytometer is governed by the dimensions of the sample analysis volume. A small volume gives a high sensitivity, but this can lead to practical problems including fabrication and clogging of the device. We describe a microfluidic impedance cytometer which uses an insulating fluid to hydrodynamically focus a sample stream of particles suspended in electrolyte, through a large sensing volume. The detection region consists of two pairs of electrodes fabricated within a channel 200 μm wide and 30 μm high. The focussing technique increases the sensitivity of the system without reducing the dimensions of the microfluidic channel. We demonstrate detection and discrimination of 1 μm and 2 μm diameter polystyrene beads and also Escherichia coli. Impedance data from single particles are correlated with fluorescence emission measured simultaneously. Data are also compared with conventional flow cytometry and dynamic light scattering: the coefficient of variation (CV) of size is found to be comparable between the systems.     

Heteroaggregation in binary mixtures of oppositely charged colloidal particles

Heteroaggregation (or heterocoagulation) rate constants have been measured in mixtures of well-characterized colloidal particles of opposite charge with multiangle static and dynamic light scattering. This technique permits routine measurements of absolute heteroaggregation rate constants, also in the presence of homoaggregation. Particularly with multiangle dynamic light scattering, one is able to estimate absolute heteroaggregation rate constants accurately in the fast aggregation regime for the first time. Heteroaggregation rate constants have also been measured over a wide range of parameters, for example, ionic strength and different surface charge densities. Amidine latex particles, sulfate latex particles, and silica particles have been used for these experiments, and they were well characterized with respect to their charging and homoaggregation behavior. It was shown that heteroaggregation rate constants of oppositely charged particles increase slowly with decreasing ionic strength, and provided the surface charge is sufficiently large, the rate constant is largely independent of the surface charge. These trends can be well described with DLVO theory without adjustable parameters.     

Some aspects of polymer colloids I. Preparation and properties of different types of latex particles

The boundary region separating a latex particle from the surrounding medium has a great influence on the properties of latex dispersions. Four types of polystyrene and polystyrene/comonomer latices differing greatly in the structure of the boundary region were prepared. The first part of a series of papers reports on the preparation of the various latex dispersions. Mean particle sizes were obtained from simple turbidity measurements, quasi-elastic light scattering, and electron micrographs. The behavior of the particles in the centrifugal force field is a simple tool for detecting aggregation tendencies that are not directly related to salt stability. The BET-surface area agrees with the area calculated from the mean particle size when a sharp boundary and smooth surface is developed between the particle and the surrounding medium. In the case of particles with extended boundary regions (core/shell particles or particles with hairy envelopes), film formation reduces the specific surface area. Removal of soluble oligomers and polymers from the boundary region during subsequent treatments (purification and centrifugation before freeze-drying) can increase the surface area considerably.     

Structural changes of latex particles of ethyl acrylate—methacrylic acid copolymers during neutralization in the presence of methanol

Using a combination of static light scattering, potentiometry, and viscometry, structural changes of latex particles of ethyl acrylate—methacrylic acid (20–70 wt%) copolymers during neutralization in the presence of methanol were investigated. It was found that the latex particles disintegrate into small subparticles, swell, and at a high content of methacrylic acid units dissolve. Disintegration of latex particles is explained by considering the particles as agglomerates formed during polymerization by coalescence of smaller particles.     

Counting of Escherichia coli by a microflow cytometer based on a photonic–microfluidic integrated device

Counting of Escherichia coli DH5α‐cell suspensions in PBS is performed using a microflow cytometer based on a photonic–microfluidic integrated device. Side‐scattered light signals are used to count the E. coli cells. A detection efficiency of 92% is achieved when compared with the expected count from a hemocytometer. The detection efficiency is correlated to the ratio of sample to sheath flow rates. It is demonstrated that E. coli can be easily distinguished from beads of similar sizes (2–4 μm) as their scattering intensities are different.     

Resonant effects in evanescent wave scattering of polydisperse colloids

Measurements and predictions are reported to understand large variations in evanescent wave (EW) scattering intensities between different particles from the same batch of single mode, polydisperse colloids. Measured EW scattering intensity distributions are obtained for three different micrometer sized latex particles irreversibly deposited onto glass surfaces. Predicted EW scattering intensity distributions are obtained using measured particle size distributions as input in a Mie theory for the three-dimensional scattering of a sphere under EW illumination. Good agreement is observed between measured and predicted EW scattering intensity distributions using no adjustable parameters. Our results indicate how finite polydispersity together with resonant effects produce large, nonlinear intensity variations between particles that appear to be physically and chemically uniform. Our findings allow such resonant effects to be understood and exploited in EW based particle-surface characterization techniques (e.g., using total internal reflections, surface plasmons) and chemical and biomolecular sensing applications (e.g., using whispering gallery modes).     

单分散聚丙烯酸丁酯-二氧化硅核壳粒子的制备

近年来,有机-无机核壳材料因其具有可调的光、电、磁等特性而备受关注．无机物外壳可以增强粒子的热力学稳定性、机械强度和抗拉性能．高分子乳胶粒内核具有弹性,且易成膜,外部包覆无机物的乳胶粒可结合两者特性并产生协同效应．     

Light scattering of phase separated systems by nucleation‐growth mechanisms: a model based on the Fast Fourier Transform

The problem of simulating light scattering patterns of polymerization induced phase separation processes by the mechanism of nucleation and growth is addressed with the objective of reducing the number of computations required to carry out the simulation. A method, based on the Fast Fourier Transform (FFT), that takes advantage of the spherical nature of the phase separated domains, is proposed. Contrary to the case in which the spherical particles are randomly placed in arbitrary locations in the scattering volume, the proposed computational scheme requires the locations not to be arbitrary but to belong to a previously defined equally spaced grid. This last constraint determines levels of resolution in which the simulation can be performed. The FFT based method is tested with a morphology previously generated with a model of the phase separation process. The light scattering pattern corresponding to this morphology, mainly represented through the particle size distribution of the spherical separated domains, has been simulated at different levels of resolution of the grid placed in the scattering domain and of the sizes of the domains. It has been found that the original morphology represented by a distribution with 17 different sizes can be approximated by a smaller number, while keeping the total volume of particles the same, without a noticeable loss of precision. This, together with the fact that the computations can be performed at different levels of resolution, gives the chance to explore an important number of approximations to the problem, many of which produce, using the proposed method, results that are comparable to those obtained at higher levels of resolution, with the advantage of requiring a smaller number of computations.