Mixed micelles surfactant exchange

A logical extension of this type of study, because of the natural presence of bile salts in the intestine and the presence of synthetic surfactants in formulations, is the consideration of bile salt-surfactant mixtures. One such study [118] has considered the effect of sodium glycocholate and its mixtures with NaLS and polysorbate 80 on the absorption and metabolism of a thiamine disulphide derivative, in rats (see Scheme 7.1). It had previously been shown that surfactants altered the reaction rates of the thiol-disulphide exchange reaction that these compounds undergo [119] and that o-benzoyl thiamine disulphide interacts with the lauryl sulphate anion to form a 1 2 complex this complex is broken up by sodium glycocholate to form new mixed micelles of thiamine derivatives and the surfactants. NaLS decreases /c and /c promoting the conversion of V to VII. The reduction in absorption and the decreased enzymatic deacylation are both explained by complex formation, although inactivation of intestinal esterase by... 

The chapter is organized as follows. Section II briefly recalls the theoretical aspects of micellar dynamics and the expressions of the relaxation times characterizing the main relaxation processes (surfactant exchange, micelle formation/breakdown). Section III reviews studies of micellar kinetics of various types of surfactants conventional surfactants with a hydrocarbon chain, surfactants with a fluorinated chain, and gemini (dimeric) surfactants. Section IV deals with mixed micellar solutions. Section V considers the d5mamics of solubilized systems. Section VI reviews the dynamics of sur-... 

Aniansson showed that mixed micellar solutions of binary svuTactant mixtures are characterized by three relaxation processes two fast processes associated with the exchange of the two surfactants between mixed micelles and bvdk phase (Xn and X12) and a slow process associated with the forma-tion/breakdown of the mixed micelles (X2). The basic assumptions and the methods used to derive the expressions of the... 

The continuous exchange of the surfactant molecules (as well as cosurfactant molecules in case of mixed micelles) constitutes a major dynamic process in micellar systems. The situation in microemulsions, although more complex, directly derives from that in simple micelles. For this reason, we will briefly recall here the main conclusions that have been estab-hshed concerning the micellar dynamics, reviewed in detail in Chapter 3. 

The effect of alcohol on the dynamic properties of micellar systems has been considered as a first approach toward the understanding of microemulsion systems. In mixed alcohol + surfactant micelles, the theory predicts the existence of three relaxation processes, which have been experimentally observed using chemical relaxation techniques a slow process associated with the formation/breakdown of mixed micelles and two fast processes associated with the exchange of the surfactant and alcohol, respectively, between the mixed micelles and the bulk aqueous phase. With g representing a mixed micelle with a alcohol (A) molecules and s surfactant (S) molecules, these two exchange reactions can be written in the form... 

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