Aqueous microemulsions

Non-aqueous microemulsions have been prepared by replacing water with formamide, a highly structured polar solvent [71]. Formamide enhances the solubility of organic compounds and is also used as a reactant. 

Unsaturated polyesters with neutralized terminal carboxyl acid groups (EUP) are efficient emulsifiers which, at a sufficient concentration, may form aqueous microemulsions. Micro emulsions are liquid dispersions of translucent (opalescent or transparent) appearance. Their disperse phase contains particles of diameters between 20 and 80 nm which closely approaches the diameters (5-15 nm) of micelles [114]. 

Silica Gels. The acid-catalyzed alkoxide sol-gel process produces gels (17). Frib-erg and coworkers (40-50) pioneered the extension of this process to silica synthesis in microemulsions both aqueous and nonaqueous microemulsions were used. For aqueous microemulsions, experiments were conducted mostly with the SDS/ pentanol/water/acid system. A representative flow diagram is shown in Figure 2.2.9. The nonaqueous microemulsion systems utilized included CTAB/decanol/ decane/formamide and AOT/decane/glycerol (44-46,49,50). The experimental approach followed the sequence nonaqueous microemulsion preparation, water addition, and then TEOS addition. 

Microemulsions are thermodynamically stable, isotropically clear dispersions composed of a polar solvent, oil, a surfactant, and a cosurfactant. Microemulsions have much potential for drug delivery as very hydro-phobic molecules can be solubilized and formulated for oral administration. All of the commercial products are actually non-aqueous microemulsions, also known as microemulsion preconcentrates or SEDDS, as the polar solvent is not water. Upon contact with aqueous media such as gastrointestinal fluids, a SEDDS formulation spontaneously forms a fine dispersion or aqueous microemulsion. 

Micellar Structure and Equilibria in Aqueous Microemulsions of Methyl Methacrylate... 

As a brief conclusion it can be noted that many nonaqueous microemulsions reported do not seem to contain an organized structure, being simply molecular solutions. Since the degree of organization already in many aqueous microemulsion is low, in particular for quaternary systems containing ionic surfactant and cosurfactant, this is not really surprising. 

Vibrational Spectroscopic Studies of Aqueous Microemulsions in SCFs... 

In general, intramolecularly crossHnked macromolecules, or microgels, can be prepared by aqueous microemulsion copolymerization of mono- and... 

The protein acrylodan-labeled bovine serum albumin (BSA-Ac) was solubilized into water-in-C02 microemulsions created with the PFPE surfactant mentioned in the previous section [73]. This particular protein was chosen because BSA is moderately large (67,000 Da) and the strong Ac fluorescence provides a measure of both BSA conformation and concentration in solution. Upon forming a microemulsion with PFPE, the BSA-Ac fluorescence is very strong and similar to that of native BSA-Ac in buffer at pH 7.0, as shown in Fig. 15. After recovery, the BSA-Ac is still recognized by the BSA antibody. These results show that BSA-Ac is solubilized within the aqueous microemulsion droplets in an environment similar to that of bulk buffered water and remains biologically active. 

Tsakova, V., S. Winkels, and J.W. Schultze. 2001. Anodic polymerization of 3,4-ethylenedioxythio-phene from aqueous microemulsions. Electrochim Acta 46 (5) 759-768. 

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