Nonionic microemulsions

The ultralow interfacial tension can be produced by using a combination of two surfactants, one predominantly water soluble (such as sodium dodecyl sulfate) and the other predominantly oil soluble (such as a medium-chain alcohol, e.g., pentanol or hexanol). In some cases, one surfactant may be sufficient to produce the microemulsion, e.g., Aerosol OT (dioctyl sulfosuccinate), which can produce a W/O microemulsions. Nonionic surfactants, such as alcohol ethoxylates, can also produce O/W microemulsions, within a narrow temperature range. As the temperature of the system increases, the interfacial tension decreases, reaching a very low value near the phase inversion temperature. At such temperatures, an O/W microemulsion may be produced. 

Many solutions of common nonionic surfactants and water separate into two phases when heated above a certain temperature (the cloud point), and some investigators call the phase of greater surfactant concentration, a microemulsion. Thus, there is not even universal agreement that a microemulsion must contain oil. 

S. Ezrahi, E. Wachtel, A. Aserin, N. Garti. Structural polymorphism in a four component nonionic microemulsion. J Coll Interface Sci 797 277-290, 1997. 

Results described in the literature have resulted in several patents, such as one for the improvement of the transport of viscous crude oil by microemulsions based on ether carboxylates [195], or combination with ether sulfate and nonionics [196], or several anionics, amphoterics, and nonionics [197] increased oil recovery with ether carboxylates and ethersulfonates [198] increased inversion temperature of the emulsion above the reservoir temperature by ether carboxylates [199], or systems based on ether carboxylate and sulfonate [200] or polyglucosylsorbitol fatty acid ester [201] and eventually cosolvents which are not susceptible for temperature changes. Ether carboxylates also show an improvement when used in a C02 drive process [202] or at recovery by steam flooding [203]. 

The phase inversion temperature (PIT) method is helpful when ethoxylated nonionic surfactants are used to obtain an oil-and-water emulsion. Heating the emulsion inverts it to a water-and-oil emulsion at a critical temperature. When the droplet size and interfacial tension reach a minimum, and upon cooling while stirring, it turns to a stable oil-and-water microemulsion form. " ... 

Amar, I., Aserin, A., and Garti, N., Solubilization patterns of lutein and lutein esters in food grade nonionic microemulsions, J. Agric. Food Chem., 51, 4775, 2003. 

Tjandra et al. (1998) have proposed an interfacial reaction model for the kinetics of the reaction between 1-bromo octane and sodium phenoxide to give 1-phenoxyoctane in a nonionic microemulsion. In this model the microemulsion is assumed to consist of the aqueous phase and the interface is covered by a monolayer of surfactant molecules. It is thus possible to assess the interfacial area from the concentration of the surfactant in the microemulsion medium. 

Surfactant Solutions New Methods of Investigation, edited by Raoul Zana Nonionic Surfactants Physical Chemistry, edited by Martin J. Schick Microemulsion Systems, edited by Henri L Rosano and Marc Clausse Biosurfactants and Biotechnology, edited by Naim Kosaric, W. L. Cairns, and Neil C. C. Gray... 

Graciaa A. et alii, The Partitioning of Nonionic and Anionic Surfactant Mixtures Between Oil/Microemulsion/Water Phases , n° SPE 13 030, Houston, 1984. 

Liu, J., Han, B., Li, G., Zhang, X., He, J. and Liu, Z. (2001) Investigation of nonionic surfactant Dynol-604 based reverse microemulsions formed in supercritical carbon dioxide. Langmuir,... 

Y203 Eu nanoparticles for potential use in FEDs have been prepared in nonionic reverse microemulsions.124 The particles were synthesized by the reaction between aqueous yttrium nitrate, europium nitrate, and ammonium hydroxide, by bulk precipitation in the reverse microemulsion... 

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. 

Ethoxylated fatty esters, emulsifiers, detergents, and dispersants, 8 710t Ethoxylated nonionic surfactants, microemulsions based on, 16 428 Ethoxylated surfactants, 24 142, 148 Ethoxylates, 24 149-151 Ethoxylation, fatty amines, 2 523 2-Ethoxypyridine, 21 104 Ethoxyquin, 10 854 13 42t, 51 2-Ethyl-1-butanol... 

The fluorescence polarization technique is a very powerful tool for studying the fluidity and orientational order of organized assemblies aqueous micelles, reverse micelles and microemulsions, lipid bilayers, synthetic nonionic vesicles, liquid crystals. This technique is also very useful for probing the segmental mobility of polymers and antibody molecules. 

The packing ratio also explains the nature of microemulsion formed by using nonionic surfactants. If v/a 1 increases with increase of temperature (as a result of reduction of a ), one would expect the solubilisation of hydrocarbons in nonionic surfactact to increase with temperature as observed, until v/a l reaches the value of 1 where phase inversion would be expected. At higher temperatures, va l > 1 and water in oil microemulsions would be expected and the solubilisation of water would decrease as the temperature rises again as expected. 

The rate constants for the reaction of a pyridinium Ion with cyanide have been measured in both a cationic and nonlonic oil in water microemulsion as a function of water content. There is no effect of added salt on the reaction rate in the cationic system, but a substantial effect of ionic strength on the rate as observed in the nonionic system. Estimates of the ionic strength in the "Stern layer" of the cationic microemulsion have been employed to correct the rate constants in the nonlonic system and calculate effective surface potentials. The ion-exchange (IE) model, which assumes that reaction occurs in the Stern layer and that the nucleophile concentration is determined by an ion-exchange equilibrium with the surfactant counterion, has been applied to the data. The results, although not definitive because of the ionic strength dependence, indicate that the IE model may not provide the best description of this reaction system. 

Thus, it was decided to employ a different substrate, and to that end we have followed the reaction of interphase-bound N-dodecyl 3-carbamoyl pyridinium bromide with cyanide ion at pH 11.8 (equation 1) in a cationic and in a nonionic microemulsion. 

The rate constants for the reaction of N-dodecyl-3-carbamoyl-pyridinlum ion with cyanide in both cationic and nonionic o/w microemulsions have been measured as a function of phase volume. Added salt has no effect in the cationic system, but the rate constants in the nonionic system depend upon ionic strength as would be expected for a reaction between two ions. In order to compare the two microemulsions, the ionic strength in the reaction region has been estimated using thicknesses of 2-4A. The former produces values of the effective surface potential which yield... 

L.T. Lee, D. Langevin, J. Meunier, K. Wong, and B. Cabane Film Bending Elasticity in Microemulsions Made with Nonionic Surfactants. Prog. Colloid Polymer Sci. 81, 209 (1990). 

Poprawski J, Catt M, Marquez L, Marti MJ, Salager JL, Aubry JM (2003) Application of hydrophilic-lipophilic deviation formulation concept to microemulsions containing pine oil and nonionic surfactants. Polym Int 52 629-632... 

Graciaa A, Lachaise J, Bourrel M, Osborne-Lee I, Schechter RS, Wade WH (1987) Partitioning of nonionic and anionic surfactant mixtiu es between oil/microemulsion/ water phases. SPE Reserv Eng 2 305-331... 

Binks BP, Hetcher PDl, Taylor DJF (1998) Microemulsions Stabilized by lonic/Non-ionic Sm-factant Mixtures. Effect of Partitioning of the Nonionic Surfactant into the Oil. Langmuir 14 5324-5326... 

Dye-Doped Silica Nanoparticle Synthesis Using Nonionic Surfactant-Based Microemulsion Systems... 

Silica particles synthesized in nonionic w/o microemulsions (e.g., poly-oxythylene alkyl phenyl ether/alkane/water) typically have a narrow size distribution with the average value between 25 and 75 nm [54,55]. Both water and surfactant are necessary components for the formation of stable silica suspensions in microemulsions. The amounts of each phase present in the micro emulsion system has an influence on the resulting size of the silica nanoparticle. The role of residual water (that is the water that is present in the interface between the silica particle and the surfactant) is considered important in providing stability to the silica nanoparticle in the oil... 

In another communication using w/o microemulsions containing a nonionic surfactant, it is shown that TEOS hydrolysis and siUca-particle growth occur at the same rate, indicating the growth of siUca particles is rate-controlled by the hydrolysis of TEOS [54], The rate of TEOS hydrolysis also depends on the surfactant concentration, which controls the molecular contact between hydroxyl ions and TEOS in solution. Because of the reaction-controlled growth mechanism, the silica-particle size distribution remains virtually same over the growth period. 

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