Sedimentation analysis of organic–inorganic hybrid colloids

Hybrid organic–inorganic latex particles are synthesized to combine the beneficial properties of the constituents which thus lead to synergistic improvement in the properties. The properties of hybrid particles are dependent on the successful hybridization process, thus controlling or tuning of such processes by effective characterization is immensely important. Analytical ultracentrifugation provides these characterization possibilities owing to its high statistical capability and ability to characterize multiple parameters. The use of different detection methodologies can help in generating valuable information on the overall size and density distributions of the particles. Apart from that, it is also possible to quantify the presence of any free polymer and inorganic particles in the hybrid latex which would affect the properties of hybrid latexes. By following the densities of the pure and hybrid particles, it is also possible to quantify the amounts of the constituent phases in the hybrid particles. The density gradients generated in preparative ultracentrifugation also provide additional possibilities for the characterization of the hybrid particles which have densities higher than the measurable range in the analytical ultracentrifuge. Evolution of hybrid particles can also be studied as a function of time. It also provides advantage of separation of the various fractions for further characterization.     

Fractionation and characterization of nano- and microparticles in liquid media

Submicron and micron particles present in liquid environmental, biological, and technological samples differ in their dimensions, shape, mass, chemical composition, and charge. Their properties cannot be reliably studied unless the particles are fractionated. Synthetic particles applied as components of analytical systems may also need preliminary fractionation and investigation. The review is focused on the methods for fractionation and characterization of nanoparticles and microparticles in liquid media, the most representative examples of their application, and the trends in developing novel approaches to the separation and investigation of particles. Among the separation techniques, the main attention is devoted to membrane filtration, field-flow fractionation, chromatographic, and capillary electrokinetic methods. Microfluidic systems employing the above-mentioned and other separation principles and providing a basis for the fabrication of lab-on-chip devices are also examined. Laser light scattering methods and other physical techniques for the characterization of particles are considered. Special attention is given to “hyphenated” techniques which enable the separation and characterization of particles to be performed in online modes.     

The properties of silica nanoparticles with high monodispersity synthesized in the microreactor system

A new combined micromixer/microreactor/batch reactor system for the synthesis of monodisperse silica particles was demonstrated, which showed superiorities over the batch reactor. The silica nanoparticles with different sizes (ranging from 20 nm to 2 μm) and size distributions could be controllably synthesized by varying the reaction temperature and reaction time. The narrowest size distribution of the silica particles was synthesized at 60 °C. The transmission electron microscopy characterization showed that the sphericities of silica particles got better as the particle size increased. Thermal gravimetry–differential thermal analysis and Fourier transform infrared characterization indicated that the amount of ethoxy groups of silica particles decreased and the hydroxyl groups increased with the reaction time increasing. And the hydroxyl groups in silica particles increased with the reaction temperature rising.     

Characterization of advanced morphologies in polymer dispersions by AUC and HDC

Polymer latex particles are used in a wide spectrum of applications that are directly influenced by the surface characteristics as well as particle size and size distribution of these polymer particles. Accurate analysis of such characteristics is required to efficiently control the behavior of such particles. Analytical ultracentrifugation (AUC) and hydrodynamic chromatography (HDC) are the particle characterization methods of high relevance owing to their statistical ability, and the combination of these two techniques also allows to generate information about the surface morphology of the particles. Such a comparison is facilitated owing to different principles of particle characterization in these two methods. AUC relies on the density difference between the particles and the suspending medium to correlate to the particle size, whereas HDC is based on the measurement of hydrodynamic diameter by UV absorption. When particles functionalized by a thin layer of hydrophilic polymer are analyzed, these two methods by the virtues of their characterization principles allow to detect the presence of such a functionalizing polymer layer on the surface. Subsequently, these methods also provide accurate estimation of the thickness of such a layer. The comparisons can also be carried out as a function of time or amount of surface functionalization to tune the properties according to the requirement. In the case where a thick polymer layer is present in the surface of the particles, the comparisons are more qualitative in nature owing to the bridging and aggregation of the particles especially noticed in HDC. However, even in such a case, the combination of these methods is the only way to characterize the special morphology of the particles.     

The Optical Characteristics Method of Sedimentation Stability for Dense Magnetic Particles Suspensions

A new method for characterization of dense magnetic particles suspension is presented. Spectrophotometric method to timing determination of amounts of settled micron magnetic particles in a dense particles suspension was used. When nano particles TiO2were added to the dense magnetic suspension, sedimentation stability of the system was evidently improved.     

Inorganic membranes based on zirconium phosphate for fuel cells

In this paper we report on zirconium phosphate based inorganic membrane preparation and electrochemical characterization. The zirconium oxide microporous membranes were impregnated with colloidal particles of zirconium phosphate and were designed for application in direct methanol fuel cells. Scanning electron microscopy, thermogravimetry and impedance spectroscopy was used for membrane characterization.     

Electrically conducting polymer colloids and composites

The preparation, characterization and properties of aqueous dispersions of electrically conducting polymer particles are described. Three types of such particles have been prepared: polyacetylene, polypyrrole and polyaniline. Particles in the size range 50–500 nm (diameter) and with conductivities generally ? 1–10 S cm may be made. Composites of such particles, dispersed in a matrix polymer which is non-conducting, are also described.     

Langmuir-Blodgett films of micron-sized organic and inorganic colloids

Multilayered films starting with silica or polymer particles in the micron-size range have been prepared using the Langmuir-Blodgett technique. The polymer particles made of highly cross-linked cores and hydrophilic shells were elaborated through a precipitation polymerization method that allows formation of particles with a low polydispersity. The influence of the surface function, the differences between organic and inorganic systems, and the characterization of these materials by means of reflectance infrared spectroscopy are also discussed.     

On the use of dead-end ultrafiltration for the study of the influence of sulfate and/or silicate on particle size distribution in concentrated and partially prehydrolyzed Al(III) flocculants

Because of their great tendency towards hydrolysis, concentrated and partially prehydrolyzed Al(III) flocculants cannot be diluted as required by many physico-chemical characterization methods. In this work, the complete dead-end ultrafiltration has proven to be a useful characterization method for these products. The results presented have shown that the behavior of the membrane/solution interphase could be described by general ultrafiltration (UF) theories. In the first part of this work, the most discriminating UF method (serial UF) is chosen for the characterization of concentrated flocculants. Next, prehydrolyzed flocculants with an increasing silicate and/or sulfate content were synthesized and the influence of silicate and/or sulfate on particle size distribution was resolved by serial UF. The silicate content is correlated to the size increase of the colloidal particles in such flocculants. This is explained by the reduced effectiveness of fragmentation of aluminosilicate particles formed during flocculant synthesis as the silicate content increases. Sulfate also increases the mean size of the particles, but the mean size is not correlated to the sulfate content. The role of sulfate is apparently to prevent the dissolution of the Al hydroxide particles formed in the initial step of flocculant synthesis. UF in presence of silicate and sulfate shows that, in such cases, sulfate could also limit the aluminosilicate fragmentation leading to a greater increase of the particle size than that observed with only silicate addition.     

Fe_2O_3超微粒/硬脂酸复合LB膜的制备和表征研究

用超声分散的方法将Ｆｅ２Ｏ３超微粒分散于硬脂酸／正己烷／氯仿溶液中，用ＬＢ膜技术进行组装。结果表明：Ｆｅ２Ｏ３超微粒能均匀地分散在有机溶剂中，并且能够被硬脂酸包裹；Ｆｅ２Ｏ３超微粒／硬酯酸单分子膜的成膜性能良好，Ｆｅ２Ｏ３超微粒／硬脂酸复合ＬＢ膜具有层状结构；在Ｆｅ２Ｏ３超微粒的晶格结构和硬脂酸单分子膜的晶格结构相匹配的情况下，Ｆｅ２Ｏ３超微粒能够被有序组装。     

Preparation and characterization of strontium targets for nuclear astrophysics experiments

Journal of Radioanalytical and Nuclear Chemistry - The present paper describes preparation and characterization of strontium targets for nuclear astrophysical experiments with alpha particles...     

Grafting characterization of natural rubber latex particles: wet-STEM imaging contributions

Natural rubber latexes investigated in this study have been chemically modified by seeded emulsion polymerization. Depending on the water affinity of the monomer involved (MMA or DMAEMA), the expected result was the grafting of the corresponding polymer inside or on the surface of the latex particles. The present article focuses on the grafting characterization of these modified natural rubber latexes. In this purpose, non-imaging classical experimental methods such as dynamic light scattering and nuclear magnetic resonance have been completed by microscopy techniques, including transmission imaging in scanning electron microscopy (SEM) and a recent imaging mode called wet-STEM. It consists in transmission imaging in an Environmental SEM operating in the wet-mode, allowing transmission observations of particles suspended in a liquid layer with good resolution and contrast. In the present study, we have adopted a comparative characterization approach between a nongrafted natural rubber latex and two grafted ones. Such an approach indeed contributes to highlight the particles morphology resulting from chemical modification using either MMA or DMAEMA. Transmission images in SEM of thin foils are relatively well interpreted and are completed with wet-STEM images of latexes in their native state, bringing important contributions for grafting characterization.     

铅铬黄粒子的微胶囊化及其表面形貌的表征

研究了铅铬黄粒子的微胶囊化及其机理；探讨了对粒子表面形貌的量化表征方法．结果表明，在油包水（Ｗ／Ｏ）乳液中对铅铬黄粒子进行无机微胶囊化是一提高其耐酸、碱性的有效方法．颜料粒子的表面形貌可用其表面分形维数（Ｄ）量化表征．     

Synthesis of colloidal silica dumbbells

We describe the synthesis and characterization of stable suspensions of monodisperse fluorescently labeled silica dumbbell particles. Pure dispersions of silica dumbbells with center-to-center lengths from 174 nm to 2.3 microm were produced with a variety of aspect ratios. Individual particles in concentrated dispersions of these particles could be imaged with confocal microscopy. These particles can be used as a colloidal model system for addressing fundamental questions about crystal and glass formation of low-aspect-ratio anisotropic particles. They also have potential in photonic applications and electro-optical devices.     

Identification and characterization of organic nanoparticles in food

Interest in nanoparticles (NPs) has increased explosively over the past two decades. Using NPs, high loadings of vitamins and health-benefit actives can be achieved in food, and stable flavors as well as natural food-coloring dispersions can be developed. Detection and characterization of NPs are essential in understanding the benefits as well as the potential risks of the application of such materials in food. While many such applications are described in the literature, methods for detection and characterization of such particles are lacking. Organic NPs suitable for application in food are lipid-, protein- or polysaccharide-based particles, and this review describes current analytical techniques that are used, or could be used, for identification and characterization of such particles in food products. We divide the analytical approaches into four sections: sample preparation; separation; imaging; and, characterization.We discuss techniques and reported applications for NPs or otherwise related particle compounds. The results of this investigation show that, for a successful characterization of NPs in food, at least some kind of sample preparation will be required. While a simple sample preparation may be satisfactory for imaging techniques for known analytes, for other techniques, a further separation using chromatography, field-flow fractionation or ion-mobility separation is necessary. Subsequently, photon-correlation spectroscopy and especially mass spectrometry techniques as matrix-assisted laser desorption/ionization combined with time-of-flight mass spectrometry, seem suitable techniques for characterizing a wide variety of organic NPs.     

Janus颗粒表面活性剂的研究进展

Janus颗粒（JPs）是一类新型的具有微米或纳米尺寸、2个半球具有不同化学特性的胶体粒子。 其中,两亲性JPs在其2个半球上分别表现出亲水和疏水的特性,作为一种新型表面活性剂受到广泛的关注。 本文综述了近几年来两亲性JPs的制备方法、表面活性理论、两亲性表征方法及其在乳液聚合中的应用,并探讨了今后的研究方向。     

RAMAN STUDIES OF AEROSOL CHEMICAL REACTIONS

Since Professor Matijevité and his colleagues published pioneering work on aerosol chemical reactions, based on experiments with monodisperse aerosol generators and laminar flow reactors, there has been considerable progress in the chemical characterization of aerosol particles and the study of their chemical reactions. This paper surveys recent developments and new research on the application of Raman spectroscopy to gas/liquid and gas/solid aerosol reactions. Of particular interest are applications of the vibrating orifice aerosol generator and electrodynamic and optical levitators coupled to Raman spectrometers to explore aerosol chemistry. The systems examined include the production of polymeric microsphcrcs, the generation of metal oxide particles from alkoxide droplets, SQ2/sorbent particle reactions used for demilitarization of stick gases, chemical characterization of particle arrays, and reactions following collisions of dissimilar particles. The complications associated with the interpretation of Raman data introduced by morphology-dependent resonances in the elastically scattered light are also examined.     

核壳聚合物粒子

介绍了核壳聚合物的用途、研究手段以及合成方法，探讨了影响核壳结构形成的热力学因素、及核壳结构的形成机理。     

Electronic Structure and Size of TiO2 Nanoparticles of Controlled Size Prepared by Aerosol Methods

Summary.  A complete characterization of nanostructures has to deal both with electronic structure and dimensions. Here we present the characterization of TiO₂ nanoparticles of controlled size prepared by aerosol methods. The electronic structure of these nanoparticles was probed by X-ray absorption spectroscopy (XAS), the particle size by atomic force microscopy (AFM). XAS spectra show that the particles crystallize in the anatase phase upon heating at 500°C, whereas further annealing at 700°C give crystallites of 70% anatase and 30% rutile phases. Raising the temperature to 900°C results in a complete transformation of the particles to rutile. AFM images reveal that the mean size of the anatase particles formed upon heating at 500°C is 30 nm, whereas for the rutile particles formed upon annealing at 900°C 90 nm were found. The results obtained by these techniques agree with XRD data. Received October 5, 2001. Accepted (revised) December 6, 2001     

Stability and magnetic characterization of oleate-covered magnetite ferrofluids in different nonpolar carriers

This work describes the preparation and stability evaluation of suspensions consisting of hydrophobic magnetite nanoparticles dispersed in different organic solvents. The ferrite particles are covered by a shell of chemisorbed oleate ions following a procedure that is described in detail. The oleate-covered particles were dispersed in different organic solvents with dielectric constants, epsilon(r), ranging between 1.8 and 9, and the centrifugal field strength needed to remove particle aggregates formed during the synthesis was determined for the different liquid carriers used. A thermodynamic analysis demonstrated that the observed stability of the suspensions in liquids with epsilon(r) < 5 is well correlated with the very low lyophobic attraction between the particles. This can easily be surmounted by thermal agitation, since the van der Waals attraction is negligible. In contrast, for liquids with epsilon(r) > 9, the suspensions become unstable because of the combined action of the van der Waals and lyophobic attractions, the latter being dominant for very polar solvents. Finally, a complete magnetic characterization of the oleate-magnetite powder, as well as of several stable ferrofluids prepared with it, was carried out. From this characterization, the magnetic diameters and magnetic moments of the particles immersed in the different liquid carriers were estimated and compared to those corresponding to the dry magnetic particles. This made it possible to estimate the thickness of the nonmagnetic layer on the particles.