Microscopic interpretation of the parameters of the second order Margules function (function for describing the molar excess Gibbs free energy of the binary micelle formation): Micellisation of the binary mixture of the surfactants Triton X-100 and (1-hexadecyl)trimethylammonium-bromide in a water solution of NaCl (0.3 mol kg−1)

Abstract

With the Two Fluid Theory, using parameter (a) of the second order Margules function (the function for fitting the dependence of the molar excess Gibbs free energy of the formation of the binary mixed micelle (gije) from the micelle content (xi)) gives the microscopic meaning (interpretation). Parameters a depends on the coordination number of the surfactants for the realisation of the certain microstate at an infinitely diluted state of the micellar pseudophase and the change of the Gibbs free energy, which incorporates one particle of surfactant i from the hypothetical ideal gas state in the monocomponent micellar phase of surfactant j at a constant temperature. In the binary mixture of surfactants, Triton X-100 (TRX-100, conformationally rigid hydrogen carbon fragment)-(1-hexadecyl)trimethylammonium-bromide (HDTMA, conformationally flexible hydrogen carbon chain) was used to describe the micellisation in a water solution in the presence of NaCl (0.3 mol kg−1) at T (283.15 to 313.15) K since the dependence gije(xi) of the first order symmetrical Margules function cannot be applied, i.e., the Regular Solution Theory does not apply. The second order Margules function of gije(xi) approaches a symmetric U shaped curve as the temperature increases.