Non-ionic microemulsions

Overall rate enhancements are generally smaller in microemulsions than in micelles, and non-ionic microemulsions often give overall inhibition because a nonionic substrate will bind to the droplet and the ionic reagent will remain in the water. 

The primary aim of microemulsion research is to find the conditions under which the surfactant solubilises the maximum amounts of water and oil, i.e. the phase behaviour has to be studied. As the effect of pressure on the phase behaviour is (in general) rather weak [30 ], it is sufficient to consider the effect of the temperature. Furthermore, it hasbeen shown that simple ternary systems consisting of water, oil and non-ionic n-alkyl polyglycol ethers (QEj) exhibit all properties of complex and technically relevant systems [6]. Therefore, we will first describe the phase behaviour of ternary non-ionic microemulsions. 

In the preceding sections, the phase behaviour of rather simple ternary and quaternary non-ionic microemulsions have been discussed. However, the first microemulsion found by Schulman more than 50 years ago was made of water, benzene, hexanol and the ionic-surfactant potassium oleate [1, 3]. Winsor also used the ionic-surfactant sodium decylsulphate and the co-surfactant octanol to micro-emulsify water/sodium sulphate and petrol ether [2], In the last 30 years, in-depth studies on ionic microemulsions have been carried out [7, 8, 65, 66]. It toned out that nearly all ionic surfactants which contain one single hydrocarbon chain are too hydrophilic to build up microemulsions. Such systems can only be driven through the phase inversion if an electrolyte and a co-surfactant is added to the mixture (see below and Fig. 1.11). 

In the previous section a quinary ionic microemulsion was timed through the phase inversion by adding a short-chain alcohol as a non-ionic co-surfactant to a single-tailed ionic surfactant. In the following the short-chain alcohol is replaced by an ordinary long-chain non-ionic surfactant. It was discussed above that the temperature dependence of the phase behaviour of ionic (see Section 1.2.4) and non-ionic microemulsions (see Section 1.2.1) is inverse. Thus, one can expect that at a certain ratio 8 of non-ionic and ionic surfactants the inverse temperature trends compensate so that a temperature-insensitive microemulsion forms. It goes without saying that this property is extremely relevant in technical applications, where often mixtures of non-ionic and ionic surfactants are used. 

Bagger-Jorgensen, H., Coppola, L., Thuresson, K., Olsson, U. and Mortensen, K. (1997) Phase behavior, microstructure, and dynamics in a non-ionic microemulsion on addition of hy-drophobically end-cappedpoly(ethylene oxide). Langmuir, 13,4204-4218. 

Lade, O., Beizai, K., Sottmann, T. and Strey, R. (2000) Polymerizable non-ionic microemulsions Phase behavior of H20- -Alkyl Methacrylate- Alkyl Poly Ethylenglycol Ether (QEj). Langmuir, 16, 4122-4130. 

Sottmann, T., Lade, M., Stolz, M. and Schomacker, R. (2002) Phase behavior of non-ionic microemulsions prepared from technical-grade surfactants. Tenside Surfactants Detergents, 39 (1), 20-28. 

The preparation of sulphated zirconia designed for catalyst supports was studied by Boutonnet et al. . Zirconia prepared in microemulsion showed a pure tetragonal structure compared with zirconia prepared by an impregnation -precipitation procedure which also contained monoclinic phase. Platinum-promoted sulphated zirconia catalysts were prepared both in anionic and non-ionic microemulsions. Furthermore, the catalytic activity and selectivity for the isomerization of hexanes were tested. The catalysts produced by the microemulsion method showed a higher selectivity towards isomers but a lower activity when compared to catalysts prepared by impregnation technique. More recently, a study of zirconia synthesis from micro and macroemulsion systems has been conducted . Spherical ZrOa particles ranging from tens of nanometers to a few micrometers were produced. 

Eshuis, A. and Mellema, (. (1984) Viscoelasticity and microstructure of non-ionic microemulsions. Cdloid Polym. Sci., 262, 159-170. 

N Garti, A Aserin, I Tiunova, S Ezrahi. Sub-zero temperature behavior of water in non-ionic microemulsions. J Thermal Anal 57 63-78 (1998). 

Garti, N., Clement, V., Fanun, M., Leser, M.E. 2000. Some characteristics of sugar ester non-ionic microemulsions in view of possible food applications. J. Agric. Food Chem. 48, 3945-3956. 

Kabalnov A, Olsson U, Wennerstrom H. (1995) Salt effects on non-ionic microemulsions are driven by adsoprtion/depletion at the surfectant monolayer. JPhys Chem 99 6220-6230. 

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