Effects of additives (methanol and NaCl) from aqueous surfactant solutions on the micellisation of sodium deoxycholate and sodium cholate binary mixture in the temperature interval T = (278.15-318.15) K: The molar excess Gibbs energy and the molar Gibbs energy of the micelle formation

Micellisation of a binary mixture of sodium deoxycholate (SD) and sodium cholate (SC) is examined for the aqueous solution without additives (referent system for self- association process) and for the aqueous solution containing methanol, NaCl and methanol + NaCl in the temperature range T= (278.15-318.15) K. Critical micelle concentrations of mono-component surfactants and binary mixtures of surfactants at different molar ratios of mixing were determined experimentally. These values were used to calculate the mole fractions of building units in the binary mixed micelle, the interaction parameter, the molar excess Gibbs energy and the molar Gibbs energy of micellisation. Effects of additives in aqueous surfactants solution on the micellisation of the binary mixture can be observed in two ways, by considering the excess molar Gibbs energy (g(ij)(e)) or by analyzing the molar Gibbs energy of micellisation (Delta g(mM)(0)). The impact of methanol in aqueous solution is expressed differently over g(ij)(e) and Delta g(mM)(0), while the effect of Na+ ion is similar for both thermodynamic functions: g(ij)(e) and Delta g(mM)(0). In this paper is performed a detailed analysis of the molar Gibbs energies of micellisation: Delta g(mM)(0) (1) = RT(x(i)lncmc(i) + x(j)lncmc(j) + x(i)lnx(i) + x(j)lnx(j) + beta(x(i) - x(i)(2))) and Delta g(mM)(0) (2) = RTlncmc(ij) and their different loading with absolute errors. (C) 2020 Elsevier Ltd.