Counterion binding mixed micelles

The effects of dilution of the micellar surface charge on the rate of alkaline hydrolysis of a betaine ester surfactant have been investigated for a mixture of decyl betainate and a nonionic surfactant with a similar CMC. It was shown that the relation between micellar composition and the hydrolysis rate essentially parallels the relation between micellar composition and counterion binding to mixed micelles made up of ionic and nonionic surfactants [20]. 

Counterion Binding. The fractional counterion binding on charged mixed micelles is of fundamental interest because it gives an indication of surface charge density which is related to the mechanism of mixing nonidealities in ionic/nonionic micelles. It is also a necessary... 

The mass action model (MAM) for binary ionic or nonionic surfactants and the pseudo-phase separation model (PSM) which were developed earlier (I EC Fundamentals 1983, 22, 230 J. Phys. Chem. 1984, 88, 1642) have been extended. The new models include a micelle aggregation number and counterion binding parameter which depend on the mixed micelle composition. Thus, the models can describe mixtures of ionic/nonionic surfactants more realistically. These models generally predict no azeotropic micellization. For the PSM, calculated mixed erne s and especially monomer concentrations can differ significantly from those of the previous models. The results are used to estimate the Redlich-Kister parameters of monomer mixing in the mixed micelles from data on mixed erne s of Lange and Beck (1973), Funasaki and Hada (1979), and others. 

Counterion Binding. Counterion binding on mixed micelles is of crucial importance toward understanding the structure and electrostatic forces involved in micelle formiation involving ionic surfactants. Specific ion electrodes are effective at measuring counterion bindings... 

The same thermodynamic quantities needed for mixed micelle formation (already discussed) are also needed for mixed admicelle formation. Luckily, the monomer-admicelle equilibrium data can be fairly easily and unambiguously obtained (e.g., see Chapter 15). This should be combined with calorimetric data for a more complete thermodynamic picture of the mixed admicelle. As with micelles, counterion bindings on mixed admicelles also need to be obtained in order to account for electrostatic forces properly. Only one study has measured counterion binding on single-component admicelles (3 .), with none reported for mixed admicelles. 

For non-ionic/ionic mixed micelles the degree of counterion binding must be proportional to the mole fraction of ionic component, in contrast to experimental observations. 

Micelles are the simplest organised form of the self-assembly produced by amphiphilic molecules due to the so-called hydrophobic effect , firstly recognized by Tanford.NMR parameters experience dramatic effects as a result of the strong intermolecular interactions among the amphiphiles. In the case of isotropic liquid systems, NMR experiments can be easily performed and modelled, since many advances have been produced in the last two decades.Hence, information on critical micelle concentration (c.m.c.), molecular conformations and interactions, counterion binding, hydration can be obtained from chemical shifts, relaxation, and self-diffusion NMR measurements, also in mixed systems. 

The mean slope of the curves for the NaTC/NaTDC mixture is 18°, giving a slope of —0.18. The percentage of counterions bound to these mixed micelles is quite small, being about 1 Na" per 10 bile salt ions. The slope of log CMC-log NaCl plot for a typical anionic detergent (e.g., sodium dodecyl sulfate) is about —0.50 (141) thus, the surfactant binds more counterions than either bile salt. 

Perhaps one of the first of the very few systematic kinetic studies on the effects of mixed micelles on the bimolecular reaction rates is one on the effects of mixed CTABr/C,oE4 where C10E4 = C,oH2,(OCH2CH2)30CH2CH20H on the rate of an 8 2 reaction of methyl naphthalene-2-sulfonate (1) with counterions of cationic surfactant (Br). Pseudophase (PP) model, i.e., Equation 5.11 has been used to explain quantitatively the deaease in k bs with increase in Xp p = [C,oE4]x/([CioE4]x + [CTABrJj). In Equation 5.11, Kj is CTABr micellar binding constant of nonionic substrate 1,... 

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