共查询到20条相似文献,搜索用时 31 毫秒
1.
I-Hsiang Tseng Stephanie S. Watson Li-Piin Sung 《Journal of nanoparticle research》2011,13(5):2195-2204
Metal oxide nanoparticles are small but easily form agglomerates in suspension, depending on the strength of particle–particle
and particle–media interactions. To understand the agglomeration behavior of nanoparticles in media and relate to it to product
performance testing, measurement methods are desired to characterize highly scattering metal oxide nanoparticle suspensions
without dilution. In this article, we describe the advantages of using photocorrelation spectroscopy (PCS) in a backscattering
detection configuration to carry out a realistic agglomerate size measurement in multiple scattering media found in most metal
oxide nanoparticle suspensions. The dynamic behavior of nano-titanium dioxide (TiO2) particles in buffer solutions of different chemical composition and pH values was investigated as a sample system using
PCS. The resulting autocorrelation functions (AFs) at different time intervals, particle concentrations, and pH values were
measured at several detection angles. The AF exhibits a multi-mode relaxation time feature and the calculated hydrodynamic
diameters strongly depended on media composition and detection angle. This result indicates that the size and dispersion of
nano-TiO2 agglomerates are significantly affected by solution media. A measurement protocol for determining size and dispersion of
metal oxide particles in media is proposed and related to a performance test found in industry. 相似文献
2.
《Journal of Quantitative Spectroscopy & Radiative Transfer》1986,35(6):447-465
Computations have been performed for homogeneous and radially inhomogeneous spheres plus agglomerated structures composed of spherical primary units. The ranges of refractive index and particle size considered are typical of soot in flames. The effects of uncertainty in the refractive index and neglect of its radial distribution on inferring spherical particle sizes and concentrations from in situ light-scattering measurements are delineated. A framework is established for computing various scattering characteristics of agglomerated particles in terms of the scattering functions for spherical particles. The results achieved for agglomerates indicate that mean values of the particle concentration, number of units in an agglomerate and overall agglomerate size may be inferred from light-scattering data. 相似文献
3.
Darryl N. Williams Katie A. Gold Tracey R. Pulliam Holoman Sheryl H. Ehrman Otto C. Wilson Jr. 《Journal of nanoparticle research》2006,8(5):749-753
Magnetite nanoparticles were synthesized and functionalized by coating the particle surfaces with gum arabic (GA) to improve particle stability in aqueous suspensions (i.e. biological media). Particle characterization was performed using transmission electron microscopy (TEM) and dynamic light scattering (DLS) to analyze the morphology and quantify the size distribution of the nanoparticles, respectively. The results from DLS indicated that the GA-treated nanoparticles formed smaller agglomerates as compared to the untreated samples over a 30-h time frame. Thermogravimetric analyses indicated an average weight loss of 23%, showing that GA has a strong affinity toward the iron oxide surface. GA most likely contributes to␣colloid stability via steric stabilization. It was determined that the adsorption of GA onto magnetite exhibits Langmuir behavior. 相似文献
4.
Burkhard Stahlmecke Sandra Wagener Christof Asbach Heinz Kaminski Heinz Fissan Thomas A. J. Kuhlbusch 《Journal of nanoparticle research》2009,11(7):1625-1635
The stability of agglomerates is not only an important material parameter of powders but also of interest for estimating the
particle size upon accidental release into the atmosphere. This is especially important when the size of primary particles
is well below the agglomerate size, which is usually the case when the size of primary particles is below 100 nm. During production
or airborne transportation in pipes, high particle concentrations lead to particle coagulation and the formation of agglomerates
in a size range of up to some micrometers. Binding between the primary particles in the agglomerates is usually due to van
der Waals forces. In the case of a leak in a pressurized vessel (e.g. reactor, transport pipe, etc.), these agglomerates can
be emitted and shear forces within the leak can cause agglomerates to breakup. In order to simulate such shear forces and
study their effect on agglomerate stability within the airborne state, a method was developed where agglomerate powders can
be aerosolized and passed through an orifice under various differential pressure conditions. First results show that a higher
differential pressure across the orifice causes a stronger fragmentation of the agglomerates, which furthermore seems to be
material dependent. 相似文献
5.
AlfredP. Weber Martin Seipenbusch Joachim Binnig Gerhard Kasper 《Particle & Particle Systems Characterization》2002,19(5):300-305
For nanoparticle agglomerates, the catalytic activity may depend strongly on their structure. The influence of different parameters such as agglomerate structure, primary particle temperature history and surface preconditioning on the catalytic activity of nanoparticles was investigated. The fraction of agglomerate surface contributing to the reaction depends on the agglomerate structure and on the velocity of the reaction under investigation. For extremely fast reactions such as the oxidation of hydrogen on Pt nanoparticles, only the outermost surface (exposed surface) contributes substantially to the formation of water. For the system investigated here, the inner surface not substantially contributing to the reaction accounted for at least 70% of the total particle surface as determined from oxygen presaturation experiments of the agglomerate surface. A considerable activity loss of the platinum particles was observed on preheating the nanoparticle agglomerates. The preheating leads to an increase in the nanoparticle size by an order of magnitude due to sintering. It is unclear if this activity reduction is due to changes in the particle surface state or to a real size effect of the nanoparticles. 相似文献
6.
Maximilian Jux Benedikt Finke Thorsten Mahrholz Michael Sinapius Arno Kwade Carsten Schilde 《Journal of nanoparticle research》2017,19(4):139
Several epoxy Al(OH)O (boehmite) dispersions in an epoxy resin are produced in a kneader to study the mechanistic correlation between the nanoparticle size and mechanical properties of the prepared nanocomposites. The agglomerate size is set by a targeted variation in solid content and temperature during dispersion, resulting in a different level of stress intensity and thus a different final agglomerate size during the process. The suspension viscosity was used for the estimation of stress energy in laminar shear flow. Agglomerate size measurements are executed via dynamic light scattering to ensure the quality of the produced dispersions. Furthermore, various nanocomposite samples are prepared for three-point bending, tension, and fracture toughness tests. The screening of the size effect is executed with at least seven samples per agglomerate size and test method. The variation of solid content is found to be a reliable method to adjust the agglomerate size between 138–354 nm during dispersion. The size effect on the Young’s modulus and the critical stress intensity is only marginal. Nevertheless, there is a statistically relevant trend showing a linear increase with a decrease in agglomerate size. In contrast, the size effect is more dominant to the sample’s strain and stress at failure. Unlike microscaled agglomerates or particles, which lead to embrittlement of the composite material, nanoscaled agglomerates or particles cause the composite elongation to be nearly of the same level as the base material. The observed effect is valid for agglomerate sizes between 138–354 nm and a particle mass fraction of 10 wt%. 相似文献
7.
Jin Shen Gang Zheng Guoqiang Sun Qijun Tu 《Particle & Particle Systems Characterization》2004,21(5):411-414
Dynamic light scattering signals from particles, exhibit fractal characteristics. This feature can be used to determine the particle size. The use of the fractal dimension, as a quantitative method to analyze the properties of dynamic light scattering signals from submicron particles, is presented. The analysis is performed directly on the time‐resolved scattered intensity, and the Box Dimensions of light scattering signals of particles with diameters 100, 200, 500 and 1000 nm. The experimental results show that the fractal dimensions of light scattering signals correlate well with particle size. In the submicron size range, the smaller the particles, the larger their fractal dimensions. Compared with the PCS technique, only several hundreds of samples are required in the fractal method. Therefore, the data processing is easily accomplished. However, this method only provides the mean particle size, but not the particle size distribution. 相似文献
8.
Characterization of size, surface charge, and agglomeration state of nanoparticle dispersions for toxicological studies 总被引:5,自引:0,他引:5
Characterizing the state of nanoparticles (such as size, surface charge, and degree of agglomeration) in aqueous suspensions
and understanding the parameters that affect this state are imperative for toxicity investigations. In this study, the role
of important factors such as solution ionic strength, pH, and particle surface chemistry that control nanoparticle dispersion
was examined. The size and zeta potential of four TiO2 and three quantum dot samples dispersed in different solutions (including one physiological medium) were characterized. For
15 nm TiO2 dispersions, the increase of ionic strength from 0.001 M to 0.1 M led to a 50-fold increase in the hydrodynamic diameter,
and the variation of pH resulted in significant change of particle surface charge and the hydrodynamic size. It was shown
that both adsorbing multiply charged ions (e.g., pyrophosphate ions) onto the TiO2 nanoparticle surface and coating quantum dot nanocrystals with polymers (e.g., polyethylene glycol) suppressed agglomeration
and stabilized the dispersions. DLVO theory was used to qualitatively understand nanoparticle dispersion stability. A methodology
using different ultrasonication techniques (bath and probe) was developed to distinguish agglomerates from aggregates (strong
bonds), and to estimate the extent of particle agglomeration. Probe ultrasonication performed better than bath ultrasonication
in dispersing TiO2 agglomerates when the stabilizing agent sodium pyrophosphate was used. Commercially available Degussa P25 and in-house synthesized
TiO2 nanoparticles were used to demonstrate identification of aggregated and agglomerated samples. 相似文献
9.
《Ultrasonics sonochemistry》2014,21(3):1100-1107
The production of fenofibrate nanoparticles combining stirred media milling and ultrasonication method was investigated in the current work. The fenofibrate drug sample was first wet milled in stirred media mill for different times and subsequently processed by ultrasonication. The effects of ultrasonication time, power on final product particle sizes were studied. The pre milling by stirred media milling was resulted into reduction of comminution resistance of material. Subsequent treatment by ultrasonication produced smaller particles than obtained by stirred media milling alone. The resulting nanoparticles were found to exhibit excellent stability as investigated by particle size, zeta potential, and multiple light scattering measurement techniques. Further, qualities of nanoparticles obtained by combined approach were characterized by TEM and XRD analysis. 相似文献
10.
分形结构对随机取向烟尘团簇粒子光散射特性的影响 总被引:1,自引:0,他引:1
利用蒙特卡罗方法对不同分形维数和分形前向因子的随机取向烟尘团簇粒子的分形结构进行了仿真,采用离散偶极子近似(DDA)方法对随机取向烟尘团簇粒子的缪勒矩阵元进行了数值计算,并与球形粒子模型进行了比较,深入探讨了烟尘团簇粒子的分形维数和分形前因子对其散射特性的影响。研究表明,等效球形粒子的光散射特性与随机取向烟尘团簇粒子的光散射特性存在很大差别,并且此差别随着团簇粒子的分形维数以及分形前向因子的增大而减小;分形维数对表征团簇粒子散射特性的缪勒矩阵元的影响在一定散射角范围内均比较明显,分形前向因子对团簇粒子的缪勒矩阵元角分布的影响与分形维数的影响类似,不过其影响相对分形维数较弱。 相似文献
11.
The surface area of nanosized agglomerates is of great importance as the reactivity and health effects of such particles are
highly dependent on surface area. Changes in surface area through sintering during nanoparticle synthesis processes are also
of interest for precision control of synthesised particles. Unfortunately, information on particle surface area and surface
area dynamics is not readily obtainable through traditional particle mobility sizing techniques. In this study, we have experimentally
determined the mobility diameter of transition regime agglomerates with 3, 4, and 5 primary particles. Agglomerates were produced
by spray drying well-characterised polystyrene latex particles with diameters of 55, 67, 76, and 99 nm. Tandem differential
mobility analysis was used to determine agglomerate mobility diameter by selecting monodisperse agglomerates with the same
number of primary particles in the first DMA, and subsequently completely sintering the agglomerates in a furnace aerosol
reactor. The size distribution of the completely sintered particles was measured by an SMPS system, which allowed for the
determination of the number of primary particles in the agglomerates. A simple power law regression was used to express mobility
diameter as a function of primary particle size and the number of primary particles, and had an excellent correlation (R2 = 0.9971) with the experimental data. A scaling exponent was determined from the experimental data to relate measured mobility
diameter to surface area for agglomerates. Using this relationship, the sintering characteristics of agglomerates were also
examined for varying furnace temperatures and residence times. The sintering data agreed well with the geometric sintering
model (GSM) model proposed by Cho & Biswas (2006a) as well as with the model proposed Koch & Friedlander (1990) for sintering by viscous flow. 相似文献
12.
Mustafa M. Aslan Mustafa Pinar Mengüç Siva Manickavasagam Craig Saltiel 《Journal of nanoparticle research》2006,8(6):981-994
The size and structure of colloidal metal oxide (MgBaFeO) particles are determined using an Elliptically Polarized Light Scattering (EPLS) technique. The approach is based on a hybrid experimental/theoretical study where the experimental data are compared against predictions obtained using a T-Matrix model that accounts for particle shape irregularities. A power-law distribution function with two parameters is employed to account for the particle size distribution. The refractive index of the particles in ethyl alcohol is calculated based on the Maxwell-Garnet formula. The experiments are conducted using a second-generation nephelometer. It is shown that the current EPLS measurements can effectively be used for identification of both the shape and the size of the colloids. 相似文献
13.
基于分形理论,采用蒙特卡罗方法对随机分布的混合凝聚粒子的空间结构进行了仿真模拟。利用Bruggeman有效介质理论得到了占有不同体积份额黑碳的内混合凝聚粒子的等效复折射率。采用离散偶极子近似方法对随机分布混合凝聚粒子在内外混合状态下的吸收、散射和消光效率因子等消光特性参量进行了数值计算,深入探讨了混合方式、容积含量、入射波长以及基本粒子粒径和数量对混合凝聚粒子消光特性的影响规律。通过将所得数值结果与T矩阵方法的数值结果进行比较发现,两种数值方法计算的结果非常相近。结果表明,随机分布混合凝聚粒子的散射效率因子对混合方式非常敏感,消光效率因子对混合方式较敏感,而吸收效率因子对混合方式不敏感。随着凝聚粒子尺度参数的增大,混合方式对散射和消光效率因子的影响逐渐显著。内外混合方式下,随着黑碳体积比的增大随机分布混合凝聚粒子的吸收、散射和消光效率因子均近似线性增大,并且增大的幅度随着粒子尺度参数的增大而增大。 相似文献
14.
S. E. Kichanov A. Kh. Islamov S. A. Samoilenko D. P. Kozlenko A. V. Belushkin V. S. Gurin G. P. Shevchenko E. E. Trusova L. A. Bulavin B. N. Savenko 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2014,8(1):98-103
The features of the formation of Ce-Ti-O complex oxide nanoclusters in a silicate glass are studied by means of the small-angle neutron scattering technique. It is found that bounded regions of density fluctuation of the glass material are formed in the initial glass matrix without the addition of titanium and cerium oxides. These regions could serve as nucleation centers for oxide clusters of cerium and titanium upon their introduction into the matrix. The calculated average size of these inhomogeneities does not exceed 30 ± 1 nm, and their surface volume equals 0.72 ± 3 nm3. A structural mechanism for Ce-Ti-O oxide formation in a silicate glass, in which the nanoclusters are formed within a bounded region of glass material inhomogeneities at low concentrations of the initial cerium oxide (CeO2), is proposed. At high cerium oxide concentrations, oxide nanocluster growth occurs predominantly on the surface of these inhomogeneities. This leads to a sharp change in the nanocluster sizes and their fractal dimension. 相似文献
15.
Julián Alberto Gallego-Urrea Julia Hammes Geert Cornelis Martin Hassellöv 《Journal of nanoparticle research》2014,16(5):1-17
The fundamental properties and processes that govern nanoparticle behavior in colloidal dispersions are critical to predict their performance in applications and also their environmental and health implications. Illite is a platy clay mineral that is present in large amounts in aquatic environments and can be used as a model natural particle for environmental risk assessment. However, the high-aspect ratio of illite makes conventional analysis, usually assuming a spherical size, insufficient for the assessment of shape-dependent properties. In the current paper, a multimethod characterization of a suspension of illite particles was done using atomic force microscopy, scanning electron microscopy, dynamic light scattering (DLS), nanoparticle tracking analysis, differential centrifugal sedimentation, and centrifugal-field flow fractionation coupled to multiangle light scattering and DLS. The relation between the different measurands was investigated, and the effect of the shape on the equivalent particle size was reported. While some of the used techniques are capable of assessing the aspect ratio of illite, the results confirm the need for multiple techniques and analysis of different types of measurands especially for high-aspect-ratio particles. 相似文献
16.
Zygmunt?J.?Jakubek Maohui?Chen Martin?Couillard Tianyang?Leng Leslie?Liu Shan?Zou Ulrich?Baxa Jeffrey?D.?Clogston Wadood?Y.?Hamad Linda?J.?Johnston
Cellulose nanocrystals (CNCs) have high aspect ratios, polydisperse size distributions, and a strong propensity for aggregation, all of which make them a challenging material for detailed size and morphology characterization. A CNC reference material produced by sulfuric acid hydrolysis of softwood pulp was characterized using a combination of dynamic light scattering (DLS), atomic force microscopy (AFM), transmission electron microscopy, and X-ray diffraction. As a starting point, a dispersion protocol using ultrasonication was developed to provide CNC suspensions with reproducible size distributions as assessed by DLS. Tests of various methods for AFM sample preparation demonstrated that spin coating on a positively charged substrate maximizes the number of individual particles for size analysis, while minimizing the presence of agglomerates. The effects of sample-to-sample variability, analyst bias, and sonication on size distributions were assessed by AFM. The latter experiment indicated that dispersion of agglomerates by sonication did not significantly change the size distribution of individual CNCs in suspension. Comparison with TEM data demonstrated that the two microscopy methods provide similar results for CNC length (mean ~?80 nm); however, the particle width as measured by TEM is approximately twice that of the CNC height (mean 3.5 nm) measured by AFM. The individual crystallite size measured by X-ray diffraction is intermediate between the two values, although closer to the AFM height, possibly indicating that laterally agglomerated CNCs contribute to the TEM width. Overall, this study provides detailed information that can be used to assess the factors that must be considered in measuring CNC size distributions, information that will be useful for benchmarking the performance of different industrially sourced materials. 相似文献
17.
G. Devanand Venkatasubbu S. Ramasamy G. S. Avadhani L. Palanikumar J. Kumar 《Journal of nanoparticle research》2012,14(4):1-18
The evolution of the particle size distribution and the surface composition of silicon carbide and titanium carbide nanoparticle (NP) dispersions were studied. The pre-dispersions were prepared using two commonly used protocols for dispersion: stirring and sonication. Two dispersants were investigated (water and Pluronic F108 1?%) at two stages: pre-dispersion and during in vitro assays. Our data show that for each tested condition, different time-dependent results for the surface chemical composition as well as size and percentage of the agglomerates and the primary particles are observed. De-agglomeration and successive or simultaneous cleaning-wrapping cycles of the nanomaterial are observed and are related to the dispersion method and the medium as well as to the chemical stability of the NP surface. Biological response during in vitro assessment was also performed for one given pre-dispersion time condition and demonstrates that the preparation method significantly alters the results. 相似文献
18.
Effects of high-intensity ultrasonication on functional and structural properties of aqueous bovine serum albumin (BSA) solutions were investigated. The functional properties of BSA were altered by ultrasonication. Surface activity of BSA increased. Minimal changes were observed in the global structure of BSA but surface charge increased particularly at basic pH values (e.g. pH>9). While dynamic light scattering measurements indicated that the particle size increased up to 3.4 times after 90 min of sonication, no significant increase in the oligomeric state of BSA using blue native PAGE was observed. The amount of free sulfhydryl groups in BSA after 90 min of sonication decreased. The increased particle size and decreased number of free sylfhydryl groups may be attributed to formation of protein aggregates. Surface hydrophobicity increased and circular dichroism spectroscopy and FTIR analysis indicated changes in the secondary structure of BSA. We hypothesize that mechanical, thermal and chemical effects of ultrasonication resulted in structural changes in BSA that altered the functional properties of the macromolecule which may be attributed to the formation of an ultrasonically induced state that differs from a thermally, mechanically or solvent induced state. 相似文献
19.
Depending on the application of nanoparticles, certain characteristics of the product quality such as size, morphology, abrasion
resistance, specific surface, dispersibility and tendency to agglomeration are important. These characteristics are a function
of the physicochemical properties, i.e. the micromechanical properties of the nanostructured material. The micromechanical
properties of these nanostructured agglomerates such as the maximum indentation force, the plastic and elastic deformation
energy and the strength give information on the product properties, e.g. the efficiency of a dispersion process of the agglomerates,
and can be measured by nanoindentation. In this study a Berkovich indenter tip was used for the characterisation of model
aggregates out of sol–gel produced silica and precipitated alumina agglomerates with different primary particle morphologies
(dimension of 15–40 nm). In general, the effect of the primary particle morphology and the presence or absence of solid bonds
can be characterised by the measurement of the micromechanical properties via nanoindentation. The micromechanical behaviour
of aggregates containing solid bonds is strongly affected by the elastic–plastic deformation behaviour of the solid bonds
and the breakage of solid bonds. Moreover, varying the primary particle morphology for similar particle material and approximately
isotropic agglomerate behaviour the particle–particle interactions within the agglomerates can be described by the elementar
breaking stress according to the formula of Rumpf. 相似文献
20.
Gold nanoparticles have been studied for many biomedical applications. However, alterations in the gold nanoparticles’ environment
frequently lead to the formation of aggregates and agglomerates, which have not been well characterized. These new structures
could significantly change the biological impact of the nanoparticles, so the appropriate characterization of these structures
prior to biological administration is vital for the correct interpretation of toxicology results. By varying the solvent or
heating under pressure, four reproducible gold nanoparticles structures were created: 10 nm primary particles, aggregates
of the primary particles that contain non-reversible bonds between the individual nanoparticles, agglomerates of primary particles
that contain reversible interactions between the individual nanoparticles, and agglomerated aggregates that have reversible
bonds linking individual aggregates. Ultraviolet–visible (UV–Vis) spectroscopy, thermal gravitational analysis, and neutron
activation analysis were each found to accurately measure the concentration of the primary particles. The primary particles
measured 10 nm by dynamic light scattering (DLS) and had a spherical morphology by transmission electron microscopy (TEM)
while the aggregates measured 110 nm by DLS and had a distorted morphology by TEM. The agglomerate and aggregated agglomerate
samples both measured >1,000 nm by DLS, but the individual particles had significantly different morphologies by TEM. Multiple
other analytical techniques, including ultracentrifugation, gel electrophoresis, and X-ray diffraction, also showed unique
traits for each structure. The structural differences did not change in the presence of cell culture media or rat serum. In
addition, the primary particles, aggregates, and agglomerates each had a unique UV–Vis spectrum, allowing for an inexpensive,
rapid method to differentiate between the structures. 相似文献