Micelle formation by amine-based CO2-responsive surfactant of imidazoline type in an aqueous solution

This study presents the synthesis of a CO2-responsive surfactant namely 2‑alkyl‑1‑hydroxyethyl imidazoline (HEAnIBs n = 16, 18, 20), which exhibits satisfactory surface and adsorption properties. The micelle formation and adsorption of the above imidazoline based surfactant in aqueous solution were studied in this work. CMC, the effectiveness of surface tension reduction, the maximum surface excess concentration, the minimum area occupied per surfactant molecule at the air/water interface, and the micelle aggregation number were obtained by measuring surface tension. Dynamic light scattering indicates that when the surfactant concentration is 1.2 times the CMC, the hydrodynamic radii of the three surfactants studied were almost equal to 8 nm. Electrical conductivity measurements indicate the micellization of surfactants in aqueous solution. In addition, typical thermodynamic parameters, including ΔGm0, ΔGads0, ΔHm0, ΔSm0, ΔHmA, ΔSmA, and ΔCp,m0 were evaluated. The thermodynamic parameters show that micelle formation is entropy-and-enthalpy co-driven from 298 K to 318 K. We expect to elucidate the self-assembly of CO2-responsive surfactant in an aqueous solution.