Abstract:

Based on the particular pH-response of dynamic imine bonds, constructing pH-responsive surfactants and the self-assemblies thereof has been one of the hotspots recently in the field of physical chemistry of surfactants. However, the reports on amphoteric surfactants containing dynamic imine bonds with simple structure have been rarely seen. Herein, an aromatic aldehyde containing sulfobetaine group （FPSA, （CHO）C₆H₄OCH₂CH₂N⁺（CH₃） ₂CH₂CH₂CH₂SO₃^-） was designed and synthesized. FPSA and octylamine （OA） were used as the precursors to form an amphoteric dynamic imine surfactant （FPSA-OA, C₈H₁₇N=CH-C₆H₄OCH₂CH₂N⁺（CH₃） ₂CH₂CH₂CH₂SO₃^-） in situ in the aqueous solution. The critical micelle concentration （cmc） and the surface tension （γ） at cmc were 3.43×10^-3mol/L and 30.89 mN/m at 25 ℃, respectively. In addition, the interfacial tension at the interface of petroleum ether-water was reduced to 4.87 mN/m. All of these results indicate that the interfacial activities of FPSA-OA are quite well. The pH-response of FPSA-OA was observed, and the pH-responsive window was in the range of 8 to 12. For a sample solution of FPSA-OA （2×10^-3mol/L）, the value of γ was reduced from approximately 70 mN/m to 37 mN/m when the pH was changed from 8 to 12, and then restored to approximately 70 mN/m if the pH was changed back to 8. This transition could be steadily and reversibly carried out over 5 cycles without any remarkable variation, which implies that FPSA-OA has an excellent pH-reversibility.

Key words: pH-switchable, amphoteric surfactant, dynamic imine bond, reversible response