Characterization of particle size and size distribution of multi-sized polymer lattices by centrifugation plus quasielastic light scattering

 A method for characterizing the particle size and size distribution of multi-sized polymer lattices was developed by combining quasielastic light scattering (QELS) with a centrifuge. Lattices were first fractionated by centrifugation and the different populations of particles were separated in successive steps. The size of these particles was measured by QELS, and the mass fraction of the particles was determined gravimetrically. The particle size and size distribution of several blends of monodisperse lattices and two industrial multi-sized lattices have been measured by this method. The results show that the particle sizes obtained using this method are in good agreement with the expected particle diameters, and that the relative amounts of the different groups of particles in the blends can be accurately determined. The efficiency of centrifuge-QELS was also confirmed by comparison with other techniques such as transmission electron microscopy (TEM), QELS, field-flow fractionation (FFF) and capillary hydrodynamic fractionation (CHDF). However, this method is not suited for the analysis of continuous, broad distributions or mixtures with a high number of different populations. It is better suited for distributions with a small number of families of particles, and then can be used for preparative propose on a laboratory scale. Received: 9 October 1996 Accepted: 7 July 1997     

Assessing the effect of latex particle size and distribution on the rheological and adhesive properties of model waterborne acrylic pressure-sensitive adhesives films

The adhesive and rheological properties of model acrylic pressure-sensitive adhesive (PSA) films prepared from high solid emulsions with different particle sizes and distributions have been investigated with a customized probe tack apparatus. For each emulsion, the monomer composition and gel content were kept constant but different average particle sizes and distributions were used. Adhesive films 100 microm thick were then prepared from these emulsions and their rheological properties in the linear regime and adhesive properties were systematically characterized. Surprisingly, both the rheological and adhesive properties were found to be very dependent on the initial latex particle size distribution. A series of experiments were carried out to assess the adhesive properties of films made from blends of small- and large-particle-size latexes. Using the probe tack test, a maximum in adhesion energy of the dry films was found for 60% of small particles in the blend, a composition clearly different from that giving a minimum viscosity of the latex implying that optimizing for properties may not be equivalent to optimizing for processing in these adhesive applications. Finally, the adhesive properties of two multimodal latexes with different particle size distributions were investigated. Both gave significantly higher adhesion energies and clear evidence of a fibrillar detachment process. This important result suggests that the spatial distribution of gel domains in the dry film and the molecular connectivity between those gel domains also play an important role in controlling its adhesive properties.     

Evaluation of the degree of mixing of combinations of dry syrup, powder, and fine granule products in consideration of particle size distribution using near infrared spectrometry

We used near infrared (NIR) spectroscopy to evaluate the degree of mixing of blended dry syrup (DS) products whose particle sizes are not specified in the Revised 16th Edition of the Japanese Pharmacopoeia, and also evaluated the degree of mixing when powder products or fine granule products were added to DS products. The data obtained were used to investigate the relationship between the particle size distributions of the products studied and the degree of mixing. We found that the particle size distribution characteristics of the 15 DS products studied can be broadly classified into 5 types. Combinations of frequently prescribed products were selected to represent 4 of the 5 particle size distribution types and were blended with a mortar and pestle. The coefficient of variation (CV) decreased as the percent mass of Asverin? Dry Syrup 2% (Asverin-DS) increased in blends of Periactin? Powder 1% (Periactin) and Asverin-DS, indicating an improved degree of mixing (uniformity). In contrast, in blends of Periactin and Mucodyne? DS 33.3%, mixing a combination at a 1:1 mass ratio 40 times resulted in a CV of 20%. Other mixing frequencies and mass ratios resulted in a CV by 50% to 70%, indicating a very poor degree of mixing (poor uniformity). These results suggest that when combining different DSs, or a DS with a powder or fine granule product, the blending obtained with a mortar and pestle improves as the particle size distributions of the components approach each other and as the ranges of the distributions narrow.     

Ostwald ripening of binary alloy particles

Classical Lifshitz-Slyozov-Wagner theory is generalized for Ostwald ripening of particles composed of random binary alloy. We show that the steady state ripening process is characterized by self-similar particle size and composition distributions. The shape of particle size distribution depends on whether the process is diffusion controlled (Lifshitz-Slyozov) or reaction controlled (Wagner) and is consistent with the predictions of classical theory for one-component materials. The steady state composition distribution, in contrast, has the same functional form in both extreme cases featuring a universal dependence of the composition upon particle size. We also found that transients in particle's composition can be very quick resulting in a steady state distribution well before it is reached by particles sizes. These transients involve significant changes in particle sizes and open an opportunity for producing metastable particle size distributions of required shape.     

Hydrodynamic chromatography of latex blends

The ability to characterize the size and shape distributions of broadly polydisperse analytes is a driving force in particle size analysis. Multi-detector hydrodynamic chromatography (HDC), which has previously shown promise in its ability to characterize the size and shape of monodisperse, spherical polystyrene latex standards, is applied here to include the characterization of bi-, tri-, and tetramodal latex blends and their constituents varying in size, chemistry, and compactness. The ability of multi-detector HDC to distinguish between similar-sized particles of different chemistry is realized by the coupling of a concentration-sensitive detector and two different types of light scattering detectors. The use of both multi-angle static and quasi-elastic light scattering permits for determination of two different size parameters across the elution profiles of the blends. Combining the size information obtained from both light scattering methods provides a measure of how particle compactness changes as a function of size in a latex blend. Multi-detector HDC was shown to be a rapid and precise method for characterizing particle size, shape, and their distributions of broadly polydisperse analytes.     

Flow field-flow fractionation-inductively coupled plasma mass spectrometry of chemical mechanical polishing slurries

Alumina- and silica-based chemical mechanical polishing slurries were analyzed to demonstrate the feasibility of field-flow fractionation-inductively coupled plasma mass spectrometry (FFF-ICP-MS). After FFF separation ²⁷Al and ²⁹Si were measured by ICP-MS to obtain size distributions, mean particle size, number average-, mass average-, Z average- diameters, minimum and maximum particle sizes, dominant particle size, and particle size ranges (breadth of size distribution, and polydispersity) characteristics. Five commercial alumina and 13 silica slurry samples were characterized. Broad distributions were detected and two polydispersity calculations were compared. Most silica samples and one alumina sample show monomodal normal distributions. Asymmetric distributions were observed for a few silica and most alumina slurries. The degree of deviation from normal distribution was assessed. Mean particle sizes of alumina slurries varied between 150 and 350 nm with the maximum detected particle of less than 680 nm. Silica slurries exhibited maximum particle sizes of less than approximately 400 nm with the mean particle sizes ranging from 110 to 220 nm. Trace metals (Fe, Ti and Zr) coeluted with Al, Si; whereas, Pb appeared to be present as colloidal fractions.     

Independence of the brittle–ductile transition from the rubber particle size for impact‐modified poly(vinyl chloride)

A series of acrylic impact modifiers (AIMs) with different particle sizes ranging from 55.2 to 927.0 nm were synthesized by seeded emulsion polymerization, and the effect of the particle size on the brittle–ductile transition of impact‐modified poly(vinyl chloride) (PVC) was investigated. For each AIM, a series of PVC/AIM blends with compositions of 6, 8, 10, 12, and 15 phr AIM in 100 phr PVC were prepared, and the Izod impact strengths of these blends were tested at 23 °C. For AIMs with particle sizes of 55.2, 59.8, 125.2, 243.2, and 341.1 nm, the blends fractured in the brittle mode when the concentration of AIM was lower than 10 phr, whereas the blends showed ductile fracture when the AIM concentration reached 10 phr. It was concluded that the brittle–ductile transition of the PVC/AIM blends was independent of the particle size in the range of 55.2–341.1 nm. When the particle size was greater than 341.1 nm, however, the brittle–ductile transition shifted to a higher AIM concentration with an increase in the particle size. Furthermore, the critical interparticle distance was found not to be the criterion of the brittle–ductile transition for the PVC/AIM blends. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 696–702, 2006     

Particle size measurement of lipoprotein fractions using diffusion-ordered NMR spectroscopy

The sizes of certain types of lipoprotein particles have been associated with an increased risk of cardiovascular disease. However, there is currently no gold standard technique for the determination of this parameter. Here, we propose an analytical procedure to measure lipoprotein particles sizes using diffusion-ordered nuclear magnetic resonance spectroscopy (DOSY). The method was tested on six lipoprotein fractions, VLDL, IDL, LDL₁, LDL₂, HDL₂, and HDL₃, which were obtained by sequential ultracentrifugation from four patients. We performed a pulsed-field gradient experiment on each fraction to obtain a mean diffusion coefficient, and then determined the apparent hydrodynamic radius using the Stokes–Einstein equation. To validate the hydrodynamic radii obtained, the particle size distribution of these lipoprotein fractions was also measured using transmission electron microscopy (TEM). The standard errors of duplicate measurements of diffusion coefficient ranged from 0.5% to 1.3%, confirming the repeatability of the technique. The coefficient of determination between the hydrodynamic radii and the TEM-derived mean particle size was r ² = 0.96, and the agreement between the two techniques was 85%. Thus, DOSY experiments have proved to be accurate and reliable for estimating lipoprotein particle sizes.     

Miscibility and enzymatic degradation studies of poly(ε-caprolactone)/poly(propylene succinate) blends

In the present study the miscibility behaviour and the biodegradability of poly(ε-caprolactone)/poly(propylene succinate) (PCL/PPSu) blends were investigated. Both of these aliphatic polyesters were laboratory synthesized. For the polymer characterization DSC, ¹H NMR, WAXD and molecular weight measurements were performed. Blends of the polymers with compositions 90/10, 80/20, 70/30 and 60/40 w/w were prepared by solution-casting. DSC analysis of the prepared blends indicated only a very limited miscibility in the melt phase since the polymer-polymer interaction parameter χ₁₂ was −0.11. In the case of crystallized specimens two distinct phases existed in all studied compositions as it was found by SEM micrographs and the particle size distribution of PPSu dispersed phase increased with increasing PPSu content. Enzymatic hydrolysis for several days of the prepared blends was performed using Rhizopus delemar lipase at pH 7.2 and 30 °C. SEM micrographs of thin film surfaces revealed that hydrolysis affected mainly the PPSu polymer as well as the amorphous phase of PCL. For all polymer blends an increase of the melting temperatures and the heat of fusions was recorded after the hydrolysis. The biodegradation rates as expressed in terms of weight loss were faster for the blends with higher PPSu content. Finally, a simple theoretical kinetic model was developed to describe the enzymatic hydrolysis of the blends and the Michaelis-Menten parameters were estimated.     

Porod scattering study of coarsening in immiscible polymer blends

Studies of immiscible blend compatibilization often involve laborious microscopy methods to characterize changes in the particle size distribution with time in the melt. Here we explore a simple alternative approach based on Porod scattering from the two-phase structure. Although micron-sized particles in immiscible polymer blends are too large to be fully characterized by small-angle scattering, Porod scattering measurements of the interfacial area combined with knowledge of the blend volume fraction allows determination of an average particle diameter from a single scattering measurement. This technique is illustrated in experiments monitoring coarsening of particle size in polystyrene/poly(methyl methacrylate) blends prepared either by melt blending or solid-state shear pulverization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 3413–3420, 2005     

CE characterization of semiconductor nanocrystals encapsulated with amorphous silicium dioxide

The electrophoretic mobility of silica-encapsulated semiconductor nanocrystals (quantum dots) dependent on the pH and the ionic strength of the separation electrolyte has been determined by CE. Having shown the viability of the approach, the electrophoretic mobility mu of the nanoparticles investigated is calculated for varied zeta potential zeta, particle radius r, and ionic strength I employing an approximate analytical expression presented by Ohshima (J. Colloid Interface Sci. 2001, 239, 587-590). The comparison of calculated with measured data shows that the experimental observations exactly follow what would be expected from theory. Within the parameter range investigated at fixed zeta and I there is an increase in mu with r which is a nonlinear function. This dependence of mu on size parameters can be used for the size-dependent separation of particles. Modeling of mu as function of I and zeta makes it possible to calculate the size distribution of nanoparticles from electrophoretic data (using the peak shape of the particle zone in the electropherogram) without the need for calibration provided that zeta is known with adequate accuracy. Comparison of size distributions calculated via the presented method with size histograms determined from transmission electron microscopy (TEM) micrographs reveals that there is an excellent matching of the size distribution curves obtained with the two independent methods. A comparison of calculated with measured distributions of the electrophoretic mobility showed that the observed broad bands in CE studies of colloidal nanoparticles are mainly due to electrophoretic heterogeneity resulting from the particle size distribution.     

Particulate growth in phase-separated polymer blends

Particle coarsening was investigated in polymer blends containing a minor phase volume of 23% produced by compositional quenching. The scaling exponents for three binary blends (polystyrene/polybutadiene, polystyrene/polyisoprene, and polystyrene/S-B random copolymer) were in reasonable agreement with the expected value of 0.33. The scaling exponent for a ternary blend containing an amphiphile (polystyrene/polybutadiene/S-B block copolymer) was substantially lower at 0.14. The particle size distributions for all the blends were broader than the self-similar distribution expected for Ostwald ripening and became increasingly broad with time. These distributions fit a two parameter coalescence model in which the probability of coalescence is proportional to the particle diameter. However, Ostwald ripening appears to make some contribution, particularly at early times. © 1998 John Wiley & Sons, Inc. J. Polym. Sci. B Polym. Phys. 36: 2191–2196, 1998     

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.     

Particle size control in dendrimer-derived supported ruthenium catalysts

A high-resolution transmission electron microscopy (HRTEM) investigation of a family of supported Ru catalysts prepared from Ru hydroxyl-terminated poly(amidoamine) dendrimer-metal nanocomposite (DMN) precursors has been conducted. Ru particle sizes observed following deposition of DMNs on a HRTEM grid can be controlled within a 0.9-1.4 nm range depending on the metal-to-dendrimer molar ratio. The average particle size in this case correlates well with the theoretically predicted particle size from the molar loading of Ru in the dendrimer. Upon impregnation of Ru-DMNs on Al(2)O(3) and subsequent thermal removal of the dendrimer via reduction at 300 degrees C, significant sintering of the Ru particles was observed. Nevertheless, the resulting supported Ru particles maintained a narrow particle size distribution and average particle size below 2.5 nm. These particle sizes no longer correlate with the metal-to-dendrimer molar ratio but do correlate with the metal-to-dendrimer weight ratio, suggesting that the dendrimer may be acting as a "sintering-control" agent on the catalyst surface. This process is not affected by the surface area of the support, since almost identical particle size distributions were obtained on three different commercial supports.     

7种生物碱在不同粒径卷烟主流烟气气溶胶中的分布研究

建立了烟气气溶胶中7种生物碱的气相色谱-质谱(GC-MS)测定方法,并采用电子低压撞击器(ELPI)分12级捕集烟气气溶胶粒相物,研究了卷烟主流烟气气溶胶中7种生物碱含量和浓度的粒径分布。捕集的气溶胶样品加入氢氧化钠溶液和二氯甲烷进行碱法提取,提取液经DB-5MS弹性毛细管柱分离,选择离子监测模式测定,内标法定量。结果表明:该法检测主流烟气气溶胶中7种生物碱的相对标准偏差(RSD)为2.1%~6.4%,检出限为0.39~14.84 ng/cig,加标回收率为85.5%~124.8%。7种生物碱主要分布于0.144~0.722μm的中等粒径气溶胶粒相物中,在粒径0.431μm的粒相物中含量最高,与捕集的粒相物质量分布一致。7种生物碱在不同粒径气溶胶粒相物中的浓度基本趋于一致,其浓度随气溶胶粒径的分布无特异性。     

Preparation and characterization of particles with small differences in polydispersity

Colloidal particles are widely used both in fundamental research and in materials science. One important parameter influencing the physical properties of colloidal materials is the particle size distribution (polydispersity) of the colloidal particles. Recent work on colloidal crystallization has demonstrated that even subtle changes in polydispersity can have significant effects. In this study we present centrifugation techniques for subtly manipulating the width and the shape of the particle size distribution, for polydispersities less than 10%. We use scanning electron microscopy as well as dynamic and static light scattering to characterize the particle size distributions. We compare the results and highlight the difficulties associated with the determination of accurate particle size distributions.     

Size-dependent electrocatalytic activity of gold nanoparticles on HOPG and highly boron-doped diamond surfaces

Gold nanoparticles were prepared by electrochemical deposition on highly oriented pyrolytic graphite (HOPG) and boron-doped, epitaxial 100-oriented diamond layers. Using a potentiostatic double pulse technique, the average particle size was varied in the range from 5 nm to 30 nm in the case of HOPG as a support and between < 1 nm and 15 nm on diamond surfaces, while keeping the particle density constant. The distribution of particle sizes was very narrow, with standard deviations of around 20% on HOPG and around 30% on diamond. The electrocatalytic activity towards hydrogen evolution and oxygen reduction of these carbon supported gold nanoparticles in dependence of the particle sizes was investigated using cyclic voltammetry. For oxygen reduction the current density normalized to the gold surface (specific current density) increased for decreasing particle size. In contrast, the specific current density of hydrogen evolution showed no dependence on particle size. For both reactions, no effect of the different carbon supports on electrocatalytic activity was observed.     

Toughening behavior of polyamide-rubber blends

The impact behavior of nylon 6- rubber blends is studied by varying the rubber concentration (0–26 vol. %), rubber particle size (0.1 - 2.0 μm) and rubber properties. The brittle to tough transition shifts to lower temperatures by increasing the rubber concentration, decreasing the particle size and by lowering the modulus of the elastomer. With very small particle sizes, however, the transition temperature increases again. The toughness of the blends above their transition temperature increases with the rubber concentration, but the particle size has only some effect. Very small particle sizes decrease the impact behavior. The postulated deformation mechanism is cavitation of the rubber followed by shear deformation of the matrix.     

SEC Characterization of Au Nanoparticles Prepared through Seed-Assisted Synthesis

In this paper we report the use of size-exclusion chromatography (SEC) for rapid determination of the sizes and size distributions of Au nanoparticles (NPs) prepared by seed-assisted synthesis. Analytical separation of Au NPs was performed in a polymer-based column of pore size 400 nm. We characterized the sizes and size distributions of the Au NPs by using 10 mM sodium dodecyl sulfate (SDS) as mobile phase and obtained a linear relationship (R ² = 0.986) between retention time and size of Au NPs within the range 9.8–79.1 nm; the relative standard deviations of these retention times were less than 0.3%. These separation conditions were used to characterize the sizes and size distributions of Au NPs prepared by seed-assisted synthesis. In addition to observing the elution times of the Au NPs we also simultaneously characterized their size-dependent optical properties by spectral measurement of the eluting peaks by use of an on-line diode-array detector (DAD), i.e., monitoring of the stability of the Au NP products. By using this approach we found the presence of SDS was beneficial in stabilizing the synthesized Au NPs. We also found that the volume of Au metal ions used affected the sizes of the final products. SEC seems an efficient tool for characterizing the sizes of NPs fabricated by seed-assisted synthesis.     

Reaction‐induced phase separation in epoxy/polysulfone/poly(ether imide) systems. II. Generated morphologies

Epoxy–aromatic diamine formulations are simultaneously modified with two immiscible thermoplastics (TPs), poly(ether imide) (PEI) and polysulfone (PSF), in concentrations ranging from 5 to 15 wt %. The epoxy monomer is based on diglycidyl ether of bisphenol A and the aromatic diamines (ADs) are either 4,4′‐diaminodiphenylsulfone (DDS) or 4,4′‐methylenebis(3‐chloro 2,6‐diethylaniline) (MCDEA). Using phase diagrams developed in Part I of this series, thermal cycles are selected to generate different morphologies. It is found that, whatever the AD employed, a particulate morphology is obtained when curing blends that are initially homogeneous. In the case of DDS‐cured blends, a unimodal particle size distribution of PSF and PEI dispersed in a continuous epoxy‐rich phase is observed. By contrast, the MCDEA‐cured blends show a bimodal particle size distribution for all PSF/PEI relations that are analyzed. A completely different morphology, characterized by a distribution of irregular TP‐rich domains dispersed in an epoxy‐rich phase (double phase morphology), is obtained when curing blends that are initially immiscible. An X‐ray analysis of the different phases makes it possible to determine their qualitative composition. The dynamic mechanical behavior of fully cured blends is also discussed. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 3964–3975, 2004