Reverse micelles definition

A structure formed by the reversible association of am-phiphiles in apolar solvents. In inverted micelles, the polar portion of the amphiphile is concentrated in the interior of the macrostructure. Such association usually occurs with aggregation and is not typically characterized by a definite nucleation stage. Thus, inverted micelles (also referred to as inverse or reverse micelles) often fail to exhibit critical micelle concentration behavior. See Micelle... 

The kinetics and thermodynamics of the solubilization and localization of guest molecules into reverse micelles in lubricants are little known. Questions such as What are the driving forces responsible for the uptake of molecules into reverse micelles What are the kinetic steps in solubilization Where is the location of the guest molecules in a water pool or interface - all still await a definitive answer (Luisi et al., 1988 Pawlak, 2001 Willermet, 1998). 

Biological systems are, by definition, multicomponent systems. One should keep in mind the difficulties of constructing molecular level pictures that satisfactorily describe systems such as a protein in a reverse micelle or a protein in a concentrated aqueous salt solution, which are certainly much simpler than anhydrobiotic organisms, for example. It is not clear to what extent the water of the hydration shell can be replaced by a third component (e.g., lipid) or what effect such replacement has on protein or enzyme properties. 

Microemulsions are systems consisting of water, oil, and amphiphile(s) that constitute a single optically isotropic and thermodynamically stable liquid solution [6]. Using this definition of microemulsions, it follows that solutions of micelles or reverse micelles with solubilized oil and water, respectively, should also be referred to as microemulsions, and these systems are therefore included in the present chapter. 

Somewhat more specific definitions of the above description came from other authors. Thus, Hauser et al. [139] found that in reverse micelles in the system AOT/isooctane/water, thirteen molecules of HjO, divided among the three types of water with differing attractions for AOT-Na, were affected by one AOT molecule two of them were more strongly bonded, while the rest eleven were weakly associated with the surfactant. Kon-No and colleagues [130, 140, 134] studied reverse microemulsions in systems AOT / (heptane / cyclohexane / isooctane /dodecane)/water and BDDAB (butyldodecyldimethylammonium bromide)/ chlorobenzene/water for examining the state of water molecules. They observed that, as discussed above, there were up to three types of water as w was increased ... 

Solubilization can be defined as the preparation of a thermodynamically stable isotropic solution of a substance normally insoluble or very slightly soluble in a given solvent by the introduction of an additional amphiphilic component or components. The amphiphilic components (surfactants) must be introduced at a concentration at or above their critical micelle concentrations. Simple micellar systems (and reverse micellar) as well as liquid crystalline phases and vesicles referred to above are all capable of solubilization. In liquid crystalline phases and vesicles, a ternary system is formed on incorporation of the solubilizate and thus these anisotropic systems are not strictly in accordance with the definition given above. 

Quaternary alkylammonium salts, used as flow reverser additives in the separation of small anions, will fall technically into the EKC definition, since the surfactant micellization is anticipated due to the electrolyte ionic strength in which the separation is conducted vide section on small ions analysis). 

As shown by the above review of the common methods used for the determination of the CMC, a series of measurements of some property of the surfactant solution as a function of surfactant concentration is usually involved. This is followed by the detection of some characteristic point - which is called the CMC. Methodical differences may originate from the choice of the characteristic point, the kind of plot on which this point is chosen, the kind of data which are plotted and the effect of the dye. The CMC is not a very sharply defined point above which properties are qualitatively different from those below. In fact, all properties of a solution in the CMC region vary in a continuous manner and so do all of their derivatives. A micelle is by definition a reversible aggregate of a large but not infinite number of monomers. The micelle formation reaction must obey the laws of chemical equilibrium and, as such, the concentration dependence of the degree of micellization has to change gradually. Consequently, all properties of the... 

---