Strong amphiphiles

Schematic phase diagrams for binary mixtures of water with a strong amphiphile, and for ternary mixtures containing oil, water, and amphiphile, are shown in Fig. 3 (adapted from Refs. 7,8). Among the many interesting...

Strong amphiphiles, 76 424 Strong metal to support interaction (SMSI), 70 42... 

The two classes of models should be considered to be complementary descriptions of amphiphilic systems. Microscopic models can describe self-assembly and explicate the differences between weak and strong amphiphiles. Interfacial models describe very strong amphiphiles and emphasize their universal behavior. 

While microscopic models do describe weak and moderately strong amphiphiles very well, they do not describe very strong ones, which are nearly insoluble in water. That is, the volume fraction of amphiphile in the microemulsion is rarely calculated to be less than a% in these models. This is adequate for the short-chain nonionic amphiphiles C,E/ but not for lipids. 

As to the first question, lattice models do exhibit oil/water inlerfacial tensions that are reduced to various degrees from the value in the absence of amphiphile. For example, in the three-component model solved within mean-field theory, a reduction on the order of 30 was found in the oil/water interfacial tension at three-phase coexistence with the microemulsion [101]. When simulated so that fluctuations were included [102], the reduction increased to about a factor of 100, which is characteristic of a weak amphiphile. Other lattice models [103] have obtained reductions as large as a factor of 800, larger than that provided by even the strong amphiphile C6E3 [104]. 

Finally, as the density of amphiphile clearly decreases with increasing L, this argument explains the correction between low interfacial tensions and strong amphiphiles, ones that can, at very low volume fraction, solubilize both oil and water. 

For very strong amphiphiles (f, is typically close to —1), the phase diagram is dominated by (lamellar liquid crystal) [72]. Slightly less negative values of fa characterize well-structured (so-called good) microemulsions. At three-phase coexistence, such a... 

In many studies, much weaker variations are observed than those exemplified above. This refers, for example, to systems of short-chain surfactants and those of polar solvents other than water. Here the segregation of components between domains (oil, water, surfactant film) is weak, and distinct structures are not formed. This can be inferred from high values of the surfactant self-diffusion coefficient, which imply a considerable role of surfactant unimer translation. Such systems are intermediate between the organized microemulsions of strongly amphiphilic surfactants and simple molecular solutions. We note that, as expected, for nonassociating solvent mixtures, the self-diffusion coefficients vary little with composition, i.e., D/Do values throughout are not too different from unity. 

On the whole, so far, RTILs are studied as potential solubilizing media or the constituent of dominant or continuous phase. However, one should keep in mind that RTILs could be viewed as excellent candidates to undergo self-assembly and self-organization. Indeed, the inclusion of a sufficiently hydrophobic tail to the cationic moiety confers a strong amphiphilic character to them. Such a characteristic structure yields strong interaction in a polar solvent and favors the self-assembly of the IL molecules [5-8]. 

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