Submicellar and non-micellar aggregates

The simple model of micellar effects upon chemical reactivity in water assumes no effect due to monomeric surfactant [70]. This assumption is reasonable, because for 

Both explanations are reasonable. Critical micelle concentrations are decreased by addition of both electrolytes and hydrophobic non-ionic solutes to water [15]. But submicellar aggregates could coexist in solution with monomeric and micellized surfactant, although their concentration is probably low [2,23]. They could interact with, and be stabilized by, hydrophobic substrates. 

Piskiewicz [119] has developed a kinetic model of micellar catalysis, based on the Hill equation of enzyme kinetics, which assumes a cooperative interaction between reactants and surfactant to form reactive substrate-micelle complexes. This model is probably not applicable to systems in which the surfactant is in large excess over substrate, as in most micellar mediated reactions, but it gives a very reasonable explanation of the rate effects of very dilute surfactants. 

There is a great deal of qualitative evidence for rate enhancements by small hydrophobic aggregates or monomers in water, although it is often difficult to distinguish between this situation and that of induced micellization. 

One early example, that of enhanced rate of aminolysis of p-nitrophenyl-derived carboxylic esters, was originally ascribed to 1 1 hydrophobic binding of the reactants [120], but was subsequently shown to be due to self-micelhzation of the ester 

---