Aqueous Mixed Micellar Solutions

Hochepied et al. [313] reported synthesis of a compound Zno73Fe2.i8 0.0904 in nanocrystalline form from a direct micelle system . In this system, functionalized surfactants Fe(DS>2 andZn(DS)2, i.e. derivatives of Na(DS), sodium dodecyl sulfate were used for obtaining micelles in aqueous solutions. Methylamine was added to the mixed micellar solution and the system agitated for 2 h. The precipitate, gathered by centrifugation, was washed with water-ethanol solutions. The particles thus obtained were - 3-4 nm in size. 

Treiner and co-workers [81] measured partitioning of 1-pentanol to elucidate the micellar composition of two aqueous mixed anionic surfactant solutions (sodium decyl sulfate -I- sodium peifluorooctanoate and sodium dodecyl sulfate + sodium perfluorooctanoate). The partition coefficient exhibited a maximum in hydrocarbon-rich mixtures in both mixed micellar solutions. The synergistic effect was attributed to hydrocarbon-fluorocarbon repulsive interaction and found to be in accord with the regular solution model using interaction parameters determined for binaiy surfactant solutions. 

In the water-flooding process, mixed emulsifiers are used. Soluble oils are used in various oil-well-treating processes, such as the treatment of water injection wells to improve water injectivity and to remove water blockage in producing wells. The same method is useful in different cleaning processes with oil wells. This is known to be effective since water-in-oil microemulsions are found in these mixtures, and with high viscosity. The micellar solution is composed essentially of hydrocarbon, aqueous phase, and surfactant sufficient to impart micellar solution characteristics to the emulsion. The hydrocarbon is crude oil or gasoline. Surfactants are alkyl aryl... 

Winsor (17) describes how electrical conductivity varies during addition of an alcohol to an aqueous micellar solution containing some solubilized oil. Conductivity initially decreases as mixed (and probably larger) micelles containing both surfactant and alcohol are formed. When liquid crystal (presumably having a lamellar structure) starts to appear in equilibrium with the micellar solution, conductivity decreases even faster. As more alcohol is added, the aqueous solution disappears, only liquid crystal is present, and the conductivity reaches a minimum. Addition of still more alcohol results in the appearance of an oil-continuous micellar solution and an increase in conductivity. Eventually all liquid crystal disappears, the increase in conductivity ceases, and conductivity... 

For the preparation of a micellar solution, the water-insoluble drug and lipophilic excipients can be dissolved in a liquid surfactant by mixing at a relatively high temperature (43S 6flntil a clear solution is obtained. If necessary, a cosolvent can be added to aid solubility in the surfactant. Then a water or buffer solution containing hydrophilic excipients is added to the desired volume while mixing. In some cases, the aqueous solution needs to be heated to the same temperature as that > the surfactant to obtain desirable results. 

Consequently, new investigations dealing with reactions in micellar solutions composed of functional surfactants, or mixtures of inert and functional surfactants, continue to appear in the literature. An interesting study of acid-catalyzed hydrolysis of 2-(p-tetradecyloxyphenyl)-l,3-dioxolane (p-TPD) in aqueous sodium dodecyl sulfate (SDS) solutions has been reported [13]. In this case,/ -TPD behaves as a non-ionic functional surfactant and apparently forms non-ideal mixed micelles with the anionic surfactant (SDS). Based on the observed kinetic data, the authors propose that, at elevated temperatures, the thermodynamic non-ideality results in the manifestation of two populations of micelles, one rich in SDS and the other rich in/>-TPD. 

This method (Fig. 9.5 A) was set up to test, in aqueous medium and in the absence of substrate, the possible reactions between lipases and all the reagents to be tested [53, 54]. Residual lipase activity was measured separately using an emulsified substrate. Sometimes the inhibitor is incorporated into a solution of a tensio-active agent in order to create a mixed micellar interface, containing the incorporated inhibitor, and described as method A by Cudrey et al. [52]. 

Treiner et al. " have described the partitioning of a solute between a mixed micellar pseudophase and the aqueous surroundings by the equation ... 

The mechanism by means of which hydrotropes operate in surfactant solutions was elucidated by Friberg and coworkers (1970, 1971 Cox, 1981), who showed that it is due to the inhibition of the formation of surfactant liquid-crystalline phases by the hydrotrope. Since they have structures similar to those of surfactants, hydrotropes can form mixed micellar structures with surfactants. However, since their hydrophilic heads are large and their hydrophobic groups are small (their V)/ Icdo ratio [Chapter 3, Section II] is liquid-crystalline structures and thus inhibit the formation of the latter. This destruction or inhibition of the liquid-crystalline phase increases the solubility of the surfactant in the aqueous phase and the capacity of its micellar solution to solubilize material. Hydrotropic action occurs at concentrations at which the hydrotrope self-associates to form these mixed structures with the surfactant (Gonzalez, 2000). 

Interaction between the surface-active components in surfactant mixtures and with the solubilizate can both increase and decrease solubilization into the mixed micelles. Thus, the addition of small quantities of sodium dodecyl sulfate sharply decreases the solubilization of Butobarbitone by micellar solutions of a commercial POE nonionic, Ci2H2s(0C2H4)230H. The competitive interaction of the sodium dodecyl sulfate with the oxyethylene groups on the surface of the micelles of the nonionic surfactant is believed to be the cause of this phenomenon (Treiner, 1985). On the other hand, a mixture of sodium dodecyl sulfate and sorbitan monopalmitate in aqueous solution (Span 40) solubilized dimethylaminoazobenzene more than either surfactant by itself, with maximum solubilization observed at a 9 1 molar ratio of the anionic to the nonionic (Fukuda, 1958). 

Photochemical processes in heterogeneous systems, and across micelle boundaries in particular, clearly has great potential. The photolysis of amphipathic alkylcobaloximes in mixed micelles shows a co-operative effect owing to structure.The photoreduction of anthraquinone in aqueous micellar solution has been compared with that in non-aqueous solution.The dimerization of 3-(n-butyl)cyclopentenone is solvent-dependent and the ratio of isomeric products depends on surfactant concentration. It is suggested that this can be used as a means of critical micellar concentration determination. 

KEL Kelarakis, A., Ming, X.-T., Yuan, X.-F., and Booth, C., Aqueous micellar solutions of mixed triblock and diblock copolymers studied using oscillatory shear, Langmuir, 20, 2036, 2004. 

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