Problems Associated with the Treatment of Conductivity−Concentration Data in Surfactant Solutions:  Simulations and Experiments

In this paper, we propose a new approach to analyze the conductivity−concentration data of ionic surfactant solutions, in the context of the determination of micellization parameters such as critical micelle concentration and degree of counterion dissociation. The method is based on the fit of the experimental raw data to a simple nonlinear function obtained by direct integration of a Boltzmann type sigmoidal function. The advantages of this procedure as compared to that most commonly used, namely, the intersection of the data regression lines above and below the critical micelle concentration and those employing the differentiation of the experimental data, are demonstrated by means of Monte Carlo simulations combined with nonlinear fits based on the Levenberg−Marquardt algorithm. The proposed method applied well to real systems that present a very gradual transition from the premicellar to the postmicellar region, in which the break of the conductivity−concentration plots is usually hard to determine.