Activity Coefficient of Triton X100 and Brij S20 in the Infinitely Diluted Micellar Pseudophase of the Binary Micelle Triton X100–Brij S20 in the Water Phase at the Temperature Interval T = (283.15–318.15) K

Abstract

Activity coefficients of the infinitely diluted micellar pseudophase are equal to parameters of the second-order Margules function: ln φ i ∞ = a ij and ln φ j ∞ = a ji . The excess chemical potential of the infinitely diluted micellar pseudophase can be expressed using partial molar enthalpy (h i E,∞) and entropy (s i E,∞), extrapolated in the infinitely diluted state: μ i E,∞ = RT ln φ i ∞ = h i E,∞ – Ts i E,∞. The binary mixture of surfactants Triton X100–Brij S20 is not a symmetric binary mixture. In the temperature interval T = (283.15–318.15) K, the activity coefficient for Triton X100 = i in the infinitely diluted micelle pseudophase is ln φ i ∞ < 0; also, the activity coefficient for Brij S20 = j in the infinitely diluted micellar pseudophase is ln φ j ∞ < 0. Thermodynamic stabilization related to the hypothetical ideal state in the infinitely diluted state of the micellar pseudophase, originating from the limit value of the chemical potential in the case of Triton X100, is of the entropic origin (s i E,∞ > 0, h i E,∞ > 0), while for Brij S20, it is of the enthalpy origin (s j E,∞ < 0, h i E,∞ < 0).