Microemulsions inorganic reactions

It should also be noted that while very few Interfaclad inorganic reactions have been examined in microemulsion media, these studies have shown that this is a fertile field for future investigations. 

Clarke et al. showed that W/C microemulsions can be used as a new environment for inorganic chemistry by studying well-known inorganic reactions (78). Roberts et al. have recently demonstrated the production of nano-sized metallic copper particles in AOT reversed micelles in compressed... 

Although microemulsions are of great industrial importance, it is only in recent years that their role as media for organic and inorganic reactions has attracted attention [148-156]. 

Spectroscopic studies were performed on water in supercritical CO2 microemulsions using an ammonium carboxylate PFPE surfactant (24). FTIR spec-toscopy was used to identify a bulk water phase within the microemulsion capable of solubilizing ionic species and supporting inorganic reactions. In addition, the UV-visible spectrum of the solvatochromic probe methyl orange indicated three microenvironments within the microemulsions (a) a polar microenvironment like that found in dry PFPE reverse micelles (b) bulk water microenvironment and (c) an acidic microenvironment due to CO2 dissolved in water. 

Microemulsions with different structures, like micelles, reverse micelles or bicontinuous networks, can be used for several inorganic, organic [72] or catalytic reactions which require a large contact area between oil and water. Besides enzyme catalysis, this can be the formation of nanoparticles [54, 73, 74], hydro-formylation reactions [75] or polymerisations [76-78]. 

This review shows that microemulsions are of interest as media for organic reactions on several accounts. First of all they can be used as a means to overcome reagent incompatibility, which frequently occurs between a lipophilic organic compound and an inorganic salt. Used for this purpose they can be regarded as an alternative to the use of a two-phase system with added phase transfer catalyst. The concept of a micro emulsion medium and phase transfer catalysis can also be combined to give a system of very high reactivity. 

However, it is well known that micelle and microemulsion solutions can have a profound effect on reaction rates for organic (1.) and inorganic(2) reactions. In this work we report mechanistic data from microemulsion solutions that would otherwise be Inaccessible. 

Abstract This review describes how the unique nanostructures of water-in-oU (W/0), oil-in-water (0/W) and bicontinuous microemulsions have been used for the syntheses of some organic and inorganic nanomaterials. Polymer nanoparticles of diameter approximately 10-50 nm can easily be obtained, not only from the polymerization of monomers in all three types of microemulsions, but also from aWinsor l-like system. A Winsor 1-like system with a semi-continuous process can be used to produce microlatexes with high weight ratios of polymer to surfactant (up to 25). On the other hand, to form inorganic nanoparticles, it is best to carry out the appropriate chemical reactions in W/0- and bicontinuous microemulsions. 

Keywords Microemulsion polymerization Microemulsion reaction Water-in-Oil (W/O) microemulsion Oil-in-Water (0/W) microemulsion Bicontinuous microemulsion Functional membranes and inorganic/polymer nanocomposites... 

On the other hand, microemulsion system could combine hydrothermal methodology to enhance the crystallization of NPs. Yan et al. s)mthe-sized t-YVOi NPs by CTAB microemulsion assisted hydrothermal reaction (Sun et al., 2002). As a t)q)ical four-component reverse micelle system, the solution contained surfactant CTAB, cosurfactant n-hexanol, oil phase n-heptane and water phase with inorganic salt. When the W value (the molar ratio of water/CTAB) was below 16, the sizes of NPs could be mediated in the range of 9-50 nm by adjusting the... 

Another type of structurally ill-defined emulsion between water and organic compounds can be applied as an efficient reaction medium for reactions between hydrophilic inorganic salts and hydrophobic organic substrates. So-called microemulsions are particularly useful in the case where the isolation of the reaction products is not necessary. 

Particles may be formed at the inorganic-C02 interface. Inorganic suspensions of metals and metal oxides have been formed by reaction or by mixing particles stabilized by surfactants or ligands (25). Semiconductor nanoparticles have been formed through chemical reduction in water-in-C02 microemulsions. The vast number of potential interfaces formed by combination of hydrophilic, lipophilic, and C02-philic phases will continue to offer... 

Surfactants in solutions show a broad variety of microstructures caused by molecular selforganisation. The observed structures depend essentially on the physical interactions of the involved components and the composition of the mixtures. For the selection of a suitable type of reaction medium the required composition of the reaction mixture is more important than the question of whether a micellar solution, a bicontinuous microemulsion, a w/o- or an o/w-microemulsion is formed. For synthetic purposes high concentrations of reactants are indispensable in order to avoid high-energy cost for work-up procedures. Therefore, a reaction system that allows high-reactant concentrations needs to be chosen. For stoichiometric reactions involving reactant incompatibility, like nucleophilic substitution reactions with an inorganic nucleophile, often an aqueous solution of this reactant has... 

The advantages of microemulsions such as the ability to entrap hydrophihc as well as hydrophobic moieties, very high interfacial area, the ease of synthesis and scale-up and monodisperse nanostructure make them an ideal template for the synthesis of nanoparticulate systems. The use of microemulsions for various organic reactions (see Chapter 5) and for the formation of inorganic nanostructures (see Chapter 6) is being explored since the last two decades. The potential of microemulsions for synthesising pharmaceutical nanocarriers will be briefly discussed. 

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