To explore the micelle thermodynamic properties of the prepared extended amphoteric surfactant C12H25(PO)3(EO)nNH(CH2)3N+(CH3)2(CH2)2SO3- (C12P3EnNS) and the interaction behavior of the extended amphoteric surfactant (C12P3E3NS) combined with Gemini cationic surfactants C14H29N+(CH2)3H29C14·2Br- (C14-3-14), the surface properties determined by a surface tensiometer and the calculated absorption and thermodynamic properties were obtained. The critical micelle concentration (cmc) values of extended amphoteric surfactants reduce with increasing temperature and the introduction of oxypropyl (PO) and oxyethylene (EO) groups. The saturated adsorption capacity (Γmax) values show a downward trend, whereas the minimum cross-sectional area (Amin) and surface adsorption efficiency (pC20) show an opposite trend. The enthalpy change ΔHmicθ, entropy change ΔSmicθ, and Gibbs free energy change ΔGadsθ and ΔGmicθ increase with increasing temperature and the insertion of PO and EO groups. Additionally, the ΔGadsθ values are smaller than the ΔGmicθ values, indicating that surface adsorption is thermodynamically more favorable than micellization formation. Moreover, three surfactants exhibit better enthalpy-entropy compensation in micellization and have similar compensation temperatures. For the C12P3E3NS/C14-3-14 mixtures, the values of cmc and γcmc are smaller than those of either component and the cmc values of the mixtures decrease and then increase with the addition of C14-3-14, which is the lowest (0.002 mmol/L) at 50 and 40% molar fractions of C12P3E3NS, indicating their strong synergistic effect, which is controlled by electrostatic forces and hydrophobic effects. The interaction parameter values of surfactants at the surface βσ are in the range of -9.66 to -11.07, while the interaction parameter values of surfactants in the micelles βm are between -4.77 and -9.16, indicating a better synergetic effect in both surface tension reduction and micelle formation.
Zhang et al. (Thu,) studied this question.