Micellar surfactant composition prediction

The mixture CMC is plotted as a function of monomer composition in Figure 1 for an ideal system. Equation 1 can be seen to provide an excellent description of the mixture CMC (equal to Cm for this case). Ideal solution theory as described here has been widely used for ideal surfactant systems (4.6—18). Equation 2 can be used to predict the micellar surfactant composition at any monomer surfactant composition, as illustrated in Figure 2. This relation has been experimentally confirmed (ISIS) As seen in Figure 2, for an ideal system, if the ratio XA/yA < 1 at any composition, it will be so over the entire composition range. In classical phase equilibrium thermodynamic terms, the distribution coefficient between the micellar and monomer phases is independent of composition. 

Dekker et al. [170] have also shown that the steady state experimental data of the extraction and the observed dynamic behavior of the extraction are in good agreement with the model predictions. This model offers the opportunity to predict the effect of changes, both in the process conditions (effect of residence time and mass transfer coefficient) and in the composition of the aqueous and reverse micellar phase (effect of inactivation rate constant and distribution coefficient) on the extraction efficiency. A shorter residence time in the extractors, in combination with an increase in mass transfer rate, will give improvement in the yield of active enzyme in the second aqueous phase and will further reduce the surfactant loss. They have suggested that the use of centrifugal separators or extractors might be valuable in this respect. 

Micellar aggregates are considered in chapter 3 and a critical concentration is defined on the basis of a change in the shape of the size distribution of aggregates. This is followed by the examination, via a second order perturbation theory, of the phase behavior of a sterically stabilized non-aqueous colloidal dispersion containing free polymer molecules. This chapter is also concerned with the thermodynamic stability of microemulsions, which is treated via a new thermodynamic formalism. In addition, a molecular thermodynamics approach is suggested, which can predict the structural and compositional characteristics of microemulsions. Thermodynamic approaches similar to that used for microemulsions are applied to the phase transition in monolayers of insoluble surfactants and to lamellar liquid crystals. 

The many interactions that the solutes experience in a micellar chromatographic system enhances the differences among them. The possibility of using, simultaneously, the three most significant variables that affect the retention (j. e., pH, and concentrations of surfactant and modifier), will improve the capability of resolution of complex mixtures of ionic and nonionic compounds. The high accuracy in the prediction of retention factors in MLC permits the reliable and relatively rapid optimization of the composition of the mobile phase for the separation of a mixture of compounds, by using an interpretive method and a reduced number of mobile phases (at least two for one variable, four or five for two variables, and nine for three variables). 

The enclosed CD-ROM contains everything needed to run MICHROM. This software is able to take the results obtained with a set of compounds and several compositions of hydro-alcoholic micellar phases, and calculate the affinity constants to predict the results for compositions of mobile phase (surfactant concentration, modifier concentration and pH). 

A detailed physicochemical model of the micelle-monomer equilibria was proposed [136], which is based on a full system of equations that express (1) chemical equilibria between micelles and monomers, (2) mass balances with respect to each component, and (3) the mechanical balance equation by Mitchell and Ninham [137], which states that the electrostatic repulsion between the headgroups of the ionic surfactant is counterbalanced by attractive forces between the surfactant molecules in the micelle. Because of this balance between repulsion and attraction, the equilibrium micelles are in tension free state (relative to the surface of charges), like the phospholipid bilayers [136,138]. The model is applicable to ionic and nonionic surfactants and to their mixtures and agrees very well with the experiment. It predicts various properties of single-component and mixed micellar solutions, such as the compositions of the monomers and the micelles, concentration of counterions, micelle aggregation number, surface electric charge and potential, effect of added salt on the CMC of ionic surfactant solutions, electrolytic conductivity of micellar solutions, etc. [136,139]. 

Both the predicted c.m.c. and micellar composition depend on the ratio of the c.m.c.s as well as on fi. When the c.m.c.s of the single surfactants are similar, the predicted c.m.c. is very sensitive to small variations in fi. Conversely, when the ratio of the c.m.c.s is large, the predicted value of the mixed c.m.c. and the micellar composition are insensitive to variations of p. For mixtures of nonionic and ionic surfactants, p decreases with increasing electrolyte concentration. This is due to the screening of the electrostatic repulsion on the addition of electrolyte. With... 

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