Micelle dissolution rate constant

A linear dependence of the fast micelle dissolution rate constant kf on CMC for over 30 different surfactants (taken from Ref [19]) and for non-ionic ethoxylated surfactants (taken from Ref. [42]) is obtained when plotting the data on a logarithmic scale as presented in Figure 13.4. These results were obtained essentially from... 

Figure 13.4 Variation of the fast micelle dissolution rate constant

Fig. 1. Dissolution of cholesterol stones by bile salt micelles. In A the cholesterol of stones is dissolved by simple micelles (BS plus Lee). In both cases unsaturated micelles diffuse to the surface of the stones where interfacial resistance regulates the detachment of Ch molecules these saturate the micelles and in this form diffuse into the bulk polution. Plotting the dissolution rate constant against a linear correlation is obtained with k=0 at zero angular velocity.

In this dissolution model, resistance occurs at the crystal-solution interface. When dissolution rate constant is plotted against angular velocity the positive intercept on the vertical axis indicates interfacial resistance (Figure 1)[9]. Detachment of Ch molecules from the surface of the cholesterol disk (or Ch stone) is a slow process and can be influenced by the presence of lecithin in BS micelles. Higuchi et al. have shown that dissolution of ChM crystals by cholate-lecithin solutions is unaffected by variations of angular... 

In the discussion of the adsorption kinetics of micellar solutions, different micelle kinetics mechanisms are taken into account, such as formation/dissolution or stepwise aggregation/disaggregation (Dushkin Ivanov 1991). It is clear that the presence of micelles in the solution influences the adsorption rate remarkably. Under certain conditions, the aggregation number, micelle concentration, and the rate constant of micelle kinetics become the rate controlling parameters of the whole adsorption process. Models, which consider solubilisation effects in surfactant systems, do not yet exist. 

The above picture shows that to describe the kinetics of adsorption, one must take into account the diffusion of monomers and micelles as well as the kinetics of micelle formation and dissolution. Several processes may take place and these are represented schematically in Fig. 4.9. Three main mechanisms may be considered, namely formation-dissolution (Fig. 4.9 (a)), rearrangement (Fig. 4.9 (b)) and stepwise aggregation-dissolution (Fig. 4.9 (c)). To describe the effect of micelles on adsorption kinetics, one should know several parameters such as micelle aggregation number and rate constants of micelle kinetics [25]. 

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