Micellar solubility concept

The use of cationic surfactants also makes it possible to apply the concept of biphasic catalysis in oleochemistry. For instance, the Johnson-Matthey company has reported that oleic acid methyl ester or linoleic acid methyl ester can be hydroformylated in micellar media using a water-soluble rhodium complex of monocar-... 

The MEUF process is based on the formation of micelles and on the increased solubility, in a micellar solution, of an organic, which is sparingly soluble in water. The overall result is a two-phase system (a) the dispersed or discontinuous phase consisting of micelles, and (b) the continuous or aqueous phase consisting of surfactant monomers. Both these phases exist in a dynamic equdibrium. This concept of phase separation suggests that the permeate concentration should be constant. Experimental data show that this is indeed the case [57, 58]. 

In terms of micellar models, the cmc value has a precise definition in the pseudo-phase separation model, in which the micelles are treated as a separate phase. The cmc value is defined, in terms of the pseudo-phase model, as the concentration of maximnm solubility of the monomer in that particular solvent. The pseudo-phase model has a number of shortcomings however, the concept of the cmc value, as it is described in terms of this model, is very useful when discussing the association of surfactants into micelles. It is for this reason that the cmc value is, perhaps, the most frequently measnred and discussed micellar parameter [39]. 

A traditional property of micellar surfactant solutions is their ability to dissolve water-insoluble, oil-soluble materials such as hydrocarbons, esters, and certain dyes and perfumes. This property, in fact, gave early support to the concept that micelles do indeed exist in aqueous solutions of surfactants, the core of the micelles in effect providing microdroplets of liquid hydrocarbon in solution with solvent properties. 

Dijferential solubilization, where micelles interact preferentially with one of the co-crystal components, is the underlying mechanism by which otherwise unstable co-crystals achieve thermodynamic stability in micellar solutions. This concept was recently reported and applied to describe the behavior of several co-crystals." " Pharmaceutical co-crystals generally comprise a hydrophobic drug and a relatively hydrophilic co-former, thus, differential solubilization may be widely encountered. This finding has important implications for the characterization of co-crystal solution behavior and can lead to huge errors in the evaluation of co-crystal solubility and dissolution if not recognized. 

The other possibility, at first examined by Wooley and co-workers [231,232] is to crosslink the corona of the micelles. These kinds of nanoparticles are designated by shell cross-linked knedel-Hke (SCK) micelles by these authors. Wooley et al. have applied this concept to a large variety of block copolymers, mainly hydrophobic-hydrophilic copolymers with PAA or quaternized PVP as the water-soluble block, which can be chemically cross-linked in their micellar form. A similar approach has been described by Armes and co-workers [233] for the synthesis of shell cross-linked micelles where core and shell are both hydrophilic. 

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