Micelle Thermodynamic Properties and Interaction Behavior of the Prepared Extended Amphoteric Surfactant with Gemini Cationic Surfactants

To explore the micelle thermodynamic properties of the prepared extended amphoteric surfactant C 12 H 25 (PO) 3 (EO) n NH(CH 2 ) 3 N + (CH 3 ) 2 (CH 2 ) 2 SO 3 – (C 12 P 3 E n NS) and the interaction behavior of the extended amphoteric surfactant (C 12 P 3 E 3 NS) combined with Gemini cationic surfactants C 14 H 29 N + (CH 2 ) 3 H 29 C 14 ·2Br – (C 14–3–14 ), 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 (Γ max ) values show a downward trend, whereas the minimum cross-sectional area ( A min ) and surface adsorption efficiency ( pC 20 ) show an opposite trend. The enthalpy change Δ H mic θ, entropy change Δ S mic θ, and Gibbs free energy change Δ G ads θ and Δ G mic θ increase with increasing temperature and the insertion of PO and EO groups. Additionally, the Δ G ads θ values are smaller than the Δ G mic θ 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 C 12 P 3 E 3 NS/C 14–3–14 mixtures, the values of cmc and γ cmc are smaller than those of either component and the cmc values of the mixtures decrease and then increase with the addition of C 14–3–14, which is the lowest (0.002 mmol/L) at 50 and 40% molar fractions of C 12 P 3 E 3 NS, indicating their strong synergistic effect, which is controlled by electrostatic forces and hydrophobic effects. The interaction parameter values of surfactants at the surface β σ are in the range of −9.66 to −11.07, while the interaction parameter values of surfactants in the micelles β m are between −4.77 and −9.16, indicating a better synergetic effect in both surface tension reduction and micelle formation.