Micellization in non-aqueous media

Kitahara, A., Kon-No, R. Micelle formation in non aqueous media, in Colloidal dispersions and micellar behaviour. ACS-Symposia Series 9, 225 (1975)... 

Very large solvent effects arc also observed for systems where the monomers can aggregate either with themselves or another species. For example, the apparent kp for polymerizable surfactants, such as certain vinyl pyridinium salts and alkyl salts of dimethylaminoalkyl methacrylates, in aqueous solution above the critical micelle concentration (cmc) are dramatically higher than they are below the cmc in water or in non-aqueous media.77 This docs not mean that the value for the kp is higher. The heterogeneity of the medium needs to be considered. In the micellar system, the effective concentration of double bonds in the vicinity of the... 

Just as with hydrothermal synthesis, it is possible to carry out the reaction in non-aqueous media, it is possible to form micelles using alcohol as the polar phase. Using ethanol as the polar phase, it is possible to further tailor the solubihties of metal hydroxides. In the SrFei20i9 hexaferrite, simply coprecipitation strontium and iron to make the mixed metal hydroxide results in a mixed-oxide phase. Sr(OH)2 has such a high solubUity... 

Many surfactants are known to form reversed micelles in apolar media and have already provided a suitable environment for elucidating catalytic activity or conformation properties of some proteins in non aqueous media. But to conduct an extraction two conditions must be fulfilled reversed micelles must exist in the organic phase in equilibrium with an excess aqueous phase and the performance of the extraction must be significant. The nature of both surfactant and solvent, the composition... 

An understanding of the aggregation of bile salts, their acids and derivatives in non-aqueous media is crucial for providing insights into the interactions of bile salts and bile acids within hydrophobic domains such as biological membranes and mixed micelles. 

The solvent polarity (non-polarity), which determines the interactions of its molecules with polar and non-polar regions of surfactant molecules, plays an important role in the formation of micelles in non-aqueous medium. For micelle formation to take place, the medium has to be a good solvent for hydrocarbon chains only. Micelles do not form in the medium of nature similar to both parts of diphilic surfactant molecules the surfactants reveal only true solubility in such medium. Low alcohols (less than C5) which are good solvents for both polar and non-polar regions of surfactant molecules are the typical examples of such media. 

Hancer, M., Patist, A., Kean, R. T., and Murahdhara, H. S. (2002) Micellization and adsorption of phospholipids and soybean oil onto hydrophilic and hydrophobic surfaces in non-aqueous media. Colloids and Surfaces 204, 31-41. 

Table 2.5 Selected data on critical micelle concentration of surfactants in non-aqueous media [3]...

The concentration at which micelles first become detectable depends on the sensitivity of the experiment used to determine the CMC. The purpose of this chapter is to discuss the experimental methods that have been used to determine the critical micelle concentration for aqueous systems, as well as to give an overview of CMC determination techniques for surfactants in non-aqueous media. 

F.M. Fowkes, The interaction of polar molecules, micelles, and polymers in non-aqueous media, in K.Shinoda, Hd., Solvent Properties of Surfactant Solutions, Dekker. New York, 1967, pp.65-115 ... 

The main difficulties in CE analysis of cationic surfactants arise from their strong adsorption to the capillary wall and their ability to form micelles at low concentrations. The addition of organic modifiers in high amounts or separation in absolutely non-aqueous media disrupt micelle formation within the sample and also effectiveness of the organic modifier to disrupt micelles of alkylbenzyl dimethyl ammonium... 

Much remains to be learned, however, regarding the limits of applicability of the fluorescence probe technique to aggregates in non-polar media. A number of obvious experiments are conspicuous by their absence from the published literature. For example, 1-pyrene carboxaldehyde is a well known probe which has been used to measure the microscopic polarity of sodium dodecyl sulfate micelles in aqueous medium (5) there is, however, no account of its use in non-polar media. 

Riekkola ML, Wiedmar SK, Valko IE, Siren H. Selectivity in capillary electrophoresis in the presence of micelles, chiral selectors and non-aqueous media. / Chromatogr 1997 792A 13—35. 

In contrast to aqueous systems, micelle formation in non-polar media is driven by the benefit in energy rather than by an increase in entropy. The replacement of polar group - hydrocarbon interaction (as in the case of dissolution) with the interaction between polar groups upon their association into micellar core is thermodynamically beneficial. The benefit in energy upon association of polar groups is so large, that even at low concentrations true surfactant solutions contain small pre-micellar associates rather than individual surfactant molecules. 

Most investigators of micellar and related phenomena have used water as a solvent. It is abundant, cheap, and easily purified, and because biological reactions occur in aqueous media we are naturally interested in reactions in water which model biological reactions. However, micelles, or micelle-like aggregates, can form in non-aqueous solvents, and it is useful to distinguish between the normal micelles which form in solvents which have three-dimensional structure [19,20], and the so-called reverse micelles which form in apolar solvents [1,126,127]. 

The critical role of H2O in the formation of dry reverse micelles, as advocated by Eicke and others, did not however match the findings of Yu et al [79] who reported the formation of large reverse micelles when the system was dry and dissolution of the micelles in presence of water. In spite of this, the effect of even trace water on micelle formation in non-polar media cannot be ignored. Some examples of CMC of surfactants in non-aqueous solvents are provided in Table 2.5. 

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