Solutions, colloidal nonaqueous

Dispersion processing (aqueous or nonaqueous). Precursor fumed silica/silica soot dispersed in polymerizing gels or potassium sihcate aqueous solutions colloidal silica for dispersion can be prepared from aerosols as soot or fumed silica by flame hydrolysis, or other suitable methods. Examples of fumed silica are Cab-O-Sil (Cabot (7orp.) and Aerosil OX-50 (Degussa Corp.). Process pore sizes 100 to 3(X) nm. 

The traditional association colloid is of the M R" type where R" is the surfactant ion, studied in aqueous solution. Such salts also form micelles in nonaqueous and nonpolar solvents. These structures, termed inverse micelles, have the polar groups inward if some water is present [198] however, the presence of water may prevent the observation of a well-deflned CMC [198,199]. Very complex structures may be formed in nearly anhydrous media (see Ref. 200). 

Zhou Y, Itoh H, Uemura T, Naka K, Chujo Y (2002) Preparation, optical spectroscopy, and electrochemical studies of novel pi-conjugated polymer-protected stable PbS colloidal nanoparticles in a nonaqueous solution. Langmuir 18 5287-5292... 

The invention and refinement of the SFA have been among the most significant advances in experimental colloid science and have allowed researchers to identify and quantify most of the fundamental interactions occurring between surfaces in aqueous solutions as well as nonaqueous liquids. Attractive van der Waals and repulsive electrostatic double-layer forces, oscillatory (solvation or structural) forces, repulsive hydration forces, attractive hydrophobic... 

Colloidal synthesis The aqueous synthesis routes could not yield rare earth oxides directly without postheat treatment, while the dry routes usually lead to products with relatively wide size distribution and the nanocrystals could not be dispersed as colloidal solutions. Therefore, it is highly desirable to synthesize R2O3 nanocrystals in suitable nonaqueous solutions. However, the decomposition of rare earth precursor and crystallization of rare earth oxide nanocrystals would require an elevated temperature. Therefore, the solvents are usually with a high boiling point, which are called "high-boiling solvents."... 

D. Fennell Evans is the director of the Center for Interfacial Engineering and professor of chemical engineering and materials science at the University of Miimesota. He is the author of more than 180 publications on self-assembly processes in water and nonaqueous solvents, microemulsions, diffusion in liquids and micellar solutions, and characterization of surfaces using scanning probe techniques. He has published two textbooks. The Colloidal Domain and The Fundamentals of Interfacial Engineering. 

Emulsion polymerization typically refers to the polymerization of a nonaqueous material in water. The polymerization of a water-soluble material in a nonaqueous continuum has been called inverse emulsion polymerization. The inverse emulsion polymerization technique is used to synthesize a wide range of polymers for a variety of applications such as wall paper adhesive, waste water fiocculant, additives for oil recovery fluids, and retention aids. The emulsion polymerization technique involves water-soluble polymer, usually in aqueous solution, emulsified in continuous oil phase using water in oil emulsifier. The inverse emulsion is polymerized using an oil- or water-soluble initiator. The product is a colloidal dispersion of sub-microscopic particles with particle size ranging from 0.05 to 0.3 pm. The typical water-soluble monomers used are sodium p-vinyl benzene sulfonate, sodium vinyl sulfonate, 2-sulfo ethyl acrylate, acrylic acid, and acrylamide. The preferred emulsifiers are Sorbitan monostearate and the oil phase is xylene. The proposed kinetics involve initiation in polymer swollen micelles, which results in the production of high molecular weight colloidal dispersion of water-swollen polymer particles in oil. 

For both LC and IC colloids, it was demonstrated that highly charged colloids are possible even in nonaqueous media. When the fraction of ionized molecules on the particle surface is compared with the total number of adsorbed molecules on the surface, it is found that approximately 1 out of 10 adsorbed molecules is ionized. The low dielectric constant of these media compared with water is primarily responsible for a low dissociation rate of the ionizable molecules. The fact that the dissociation in the solution is also low ensures that high concentrations of ions are not available to effectively screen the particle charge and high charges or zeta potentials are attainable. 

Shinoda, K. andOgawa, T. (1967) Solubilization of water in nonaqueous solutions ofnon-ionic surfactants.. Colloid Interface Sci. 24, 56. 

Materials of interest include metals and alloys, semiconductors, ceramics and ionic solids, concrete, dielectrics and polymers, composites, biological materials including proteins and enzymes, membranes and coatings, aqueous and nonaqueous solvents and solutions, molten salts, catalytic materials, colloids, surfactants and inhibitors, and emulsions and foams. 

The removal of heavy metal ions from both natural water supplies and industrial wastewater streams is becoming increasingly important as awareness of the environmental impact of such pollutants is fiilly realized. In particular, the likelihood of such metal ions precipitating out of solution and/or coating other materials can have a profound effect on both aqueous and nonaqueous environments. There is considerable evidence in the literature that the primary mechanism for transportation of metal contaminants in aquatic systems is the movement of suspended particulate material containing the adsorbed pollutant metals [1,2]. It is also known that a strong correlation exists between the concentration of trace metals in the (aquatic) environment and the extent to which those metal ions adsorb onto colloidal substrates present in the environment [2,3], A similar correlation between the concentration of trace metals in the (aquatic) environment and their precipitation behavior is not so clear. There is, then, a well-founded need to study adsorption-related phenomena in order to understand and predict the behavior of toxic metals in the environment. 

Valentin C., Munoz M.C., Alarcdn J. Synthesis and characterization of vanadium-containing ZrSi04 solid solutions from gels. J. Sol-Gel Sci. Technol. 1999 15 221-230 Van Helden A.K., Jansen J.W., Vrij A. Preparation and characterization of spherical monodisperse silica dispersions in nonaqueous solvents. J. Colloid Interf. Sci. 1981 81 354-368 Woodhead J.L. Sol-gel processes to ceramic particles using inorganic precursors. J. Mater. Educ. 1984 6 887-925... 

Sodium borohydride is quite a strong reducing agent and therefore it has been often used for the reduction of metal salts to produce small metal particles in solution. Klabunde and co-workers performed a large amount of work on the synthesis of magnetic particles based on iron and cobalt " using borohydride reduction. For these metals however, some complications can arise if the stoichiometry is not carefully adjusted, since otherwise one can easily end up with the corresponding metal borides. Borohydride has also been applied for the reduction of noble metals, both in aqueous and in non-aqueous solution. We restrict ourselves in this section to reactions in aqueous media, while borohydride production of nonaqueous colloids is discussed in Section 2.2.1. 

Hydrolyzable salts of metal ions are used for synthesis of corresponding oxides in colloidal form by their forced hydrolysis under hydrothermal conditions [322] or in high-boiling solvents (polyols) [323], Hydrolysis in nonaqueous solutions has been applied also to metal alkoxides [324] and diketonates [325], offering a convenient route to the uncapped nanoparticles. Synthesis of oxide nanocrystals has been directed to nonaqueous approaches [326-328] mostly inspired by the success of the synthesis of high quality semiconductor nanocrystals in nonaqueous media [329]. The quality of the nanocrystals yielded by these nonaqueous solution methods is generally better than that of the nanocrystals synthesized in aqueous solutions. 

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