Model description and equations

For the mixture of two non-ionic surfactants, or the mixture of a non-ionic with an ionic surfactant, assuming that the behaviour of each surfactant is governed by the Frumkin model, the system was shown in Section 2.4 to obey the equation of state (2.35)  

Here the subscript i (i = 1, 2) refers to the surfactant molecular species, 6, = Fj03j is the surface layer coverage by i surfactant, F, is the adsorption of i surfactant, FI = yo - y is the surface pressure, yo is the surface tension of solvent. In the program, two forms of the isotherm equations are implemented  

In the experimental data, the inorganic electrolyte concentration is usually kept fixed. For any system studied, the experimental runs are performed either for fixed molar fractions x, and Xj, i.e. c, = c x,/( X, + Xj), Cj = c + 2) for fixed concentration of, say, the second 

The concentration value c = Cj + C2 is scanned through the relevant range. The numerical procedure used for the solution of the set (7.30) is described in the Manual. For each c, Eq. (7.28) is used to calculate the surface pressure or surface tension. The target function is calculated as the mean square deviation between the experimental data and the theoretical values calculated over the same set of c values. Similarly to other programs (IsoFit and lonMix), the scanning through the a,2 range was implemented rather than an automated search for the optimum a,2 value. 

Mixture of oxyethylated decyl alcohol and sodium dodecyl sulphate in 0.01 M NaCI. 

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