Excess Gibbs energy of the binary mixed micelle formation between ionic and non-ionic surfactants in the set of: Sodium-cholate, sodium-deoxycholate, Brij S10 and Brij 58 at T = (283.15-323.15) K

Molar excess Gibbs energy of mixed micelle formation (g(e)) between ionic and non-ionic surfactants in the set of the following surfactants: sodium-cholate (SC), sodium-deoxycholate (SDC), Brij S10 (BS) and Brij 58 (B58) can be described by first order Margules function. The Regular Solution Theory (RST) hypothesis of zero excess entropy cannot be accepted with these systems of investigated surfactants. Molar excess entropy is probably the result of conformational entropy, while the configurational entropy is zero, and these two facts are the bases for the description of g(e) by first order Margules function. The interaction coefficient between the different building units of the investigated binary surfactant systems has greater value than 0, which means that there are antagonistic interactions between the surfactant molecules in the mixed micelles. According to the H-1-H-1 ROESY 2D spectra there are interactions between the hydrogens from the angular methyl groups of the SC (SDC) steroid skeleton and the hydrogen from the middle and terminal part of the B58 (BS10) hydrocarbon chain in the mixed micelles. The intensities of the cross-peaks and the interaction coefficients decrease with temperature, which suggests that with temperature increase the mixed micelle becomes more diffuse, i.e. less compact. There are cross-peaks in the ROESY 2D spectra between the building units of the mixed micelles, which mean that mixed micelles are formed, but the peaks don't give information about the synergistic or antagonistic effects between the surfactants. (C) 2019 Elsevier Ltd.