Thoughts on the ideal behavior of mixed micelles and the appropriate application of regular solution theory (RST).

Solutions of mixed surfactants are often considered as solvent mixtures. Usually, mixed micellar aggregates are considered as a homogeneous mixture of solvents dispersed in a solution. But the transposition of the usual thermodynamic models of solvent mixtures to mixed micelles is not always so obvious.

Mixing behaviour of charged and non-charged surfactants described by BET isotherms.

We analysed various sets of published results concerning the mixing behaviour of charged and non-charged surfactants, beyond their aggregation threshold, by means of the BET model modified by Stokes and Robinson. This approach, which is mainly used to account for properties of concentrated aqueous salt solutions, provides a good description of the properties of mixed micelles across the complete scale of compositions between the two pure surfactants. We use analyses of the behaviour of several systems reported in the literature for illustration.

Thermodynamics of mixed micelles: Determination of the aggregate composition.

In most studies concerning surfactant mixtures, the determination of the composition of mixed micelles is often tricky. This composition can be obtained by different ways. One of them, undoubtedly the most used, supposes, a priori, that the surfactant in the micelle follows the regular solution model.

Micellar aggregation for ionic surfactant in pure solvent and electrolyte solution: nonextensive thermodynamics approach.

We show in this study that the concepts of nonextensive thermodynamics introduced and applied in a series of previous studies can be used to describe the behaviour of ionic surfactant solutions at concentrations higher than the critical micelle concentration (cmc) in pure solvents and in the presence of electrolytes. We supposed that the aggregated amphiphiles and their counter ions form two interpenetrated nonextensive phases of the same thermodynamic dimension, m, characterised by two parameters A(am) and A(CI) related to the aggregated amphiphile and the counter ion, respectively. Our experimental results and those published in the literature indicate that logarithms of the activities of the amphiphile and of its counterion vary with the quantity of aggregated monomer according to a power law.

Drop size effect on contact angle explained by nonextensive thermodynamics. Young's equation revisited.

We applied the concepts of nonextensive thermodynamics [Turmine et al., J. Phys.

Modification of the wettability of a polymeric substrate by pH effect. Determination of the surface acid dissociation constant by contact angle measurements.

The wetting properties of a substrate can be changed by chemical reaction. Here, we studied simple materials with acid-base properties, by preparing poly(vinyl chloride) films containing lauric acid. These substrates constitute simple polymeric surfaces the wettability of which can be easily controlled by the acid-base equilibrium.