Abstract:

The interfacial dilational rheological method was used to study the interfacial aggregation behavior of zwitterionic imidazole surfactant 3-(1-dodecyl-3-imidazolio)propanesulfonate(C₁₂imSP) solutions. The effect and mechanism of traditional surfactant sodium dodecyl sulfate(SDS) on the aggregation behavior of C₁₂imSP at air/water interface were explored. The results have shown that the SDS molecules tend to fill the vacancy among C₁₂imSP molecules when the C₁₂imSP molecules arrange loosely at interface, and mixed-adsorption films formed by SDS and C₁₂imSP spread on the air/water interface, correspondingly, the interfacial tension decrease dramatically. With the increase of SDS concentration, the diffusion exchange of molecules from bulk phase to interface is predominant and the interfacial layer reaches saturation adsorption gradually. Thereafter, the mixed micelles appear in the system. The “acceptance” and the further “detainment” of the rich SDS molecules in micelles to C₁₂imSP molecules as well as the larger steric hindrance of C₁₂imSP themselves lead to the C₁₂imSP molecules are very difficult to revert to the interface once they are exchanged into bulk phase. Namely, SDS almost entirely occupy the air/water interface. Obviously, the interfacial aggregation behavior of SDS/C₁₂imSP/NaCl(0.1 mol/L) system can be adjusted by tailor the system composition and thus realize the regulation to the properties of interfacial film.

Key words: ionic liquid surfactant, interface aggregation behavior, dilational rheology