Experimental and DFT studies on micellization features of anionic surface active ionic liquid and nonionic surfactant mixtures: Effect of imidazolium cations

The micellization characteristics of nonionic surfactant (Triton TX-100, p-octyl polyethylene glycol phenyl ether) and two anionic surface active ionic liquids (SAILs) were investigated by surface tension measurements, steady state fluorescence tests, dynamic light scattering (DLS), H–Nuclear magnetic resonance, and density functional theory (DFT) calculations. The anionic SAILs were 1-ethoxycarbonyl-3-methylimidazolium dodecyl sulfate ([Etmim][C12H25SO4]) and 1-ethoxycarbonyl-3-butylimidazolium dodecyl sulfate ([Etbim][C12H25SO4]). CMCmix values of SAIL/TX-100 mixtures were between CMC values of individual surfactants, and decreased with the increase of the molar fraction of TX-100. The negative β values (interaction parameter) of SAIL/TX-100 mixtures indicated good synergistic effect amid SAIL/TX-100 mixtures. [Etbim][C12H25SO4] showed stronger attractive interactions than [Etmim][C12H25SO4] during SAIL/TX-100 micellization. The mixed micelles contained a larger molar fraction of TX-100 over the entire range of composition. At same molar fraction of TX-100, X1 values of [Etbim][C12H25SO4]/TX-100 mixtures were lower than those of [Etmim][C12H25SO4]/TX-100 mixtures. With addition of SAIL, the particle sizes of SAIL/TX-100 micelles decreased. With the increase of SAIL concentrations, the particle sizes of SAIL/TX-100 micelles decreased. In presence of SAILs ([Etmim][C12H25SO4] or [Etbim][C12H25SO4]), all protons of TX-100 moved downfield. The chemical shifts of protons in [Etmim][C12H25SO4] or [Etbim][C12H25SO4] slightly moved upfield. DFT simulations demonstrated the presence of hydrogen bonds between the imidazolium cation of SAILs and EO chain of TX-100, and between sulfate anion group(-SO4-) of SAILs and hydrogen atoms in TX-100. The information will shed light on the rapid screening of novel anionic SAIL/surfactant mixtures for practical applications. © 2021