Controllable Organization of a Carboxylic Acid Type Gemini Surfactant at Different pH Values by Adding Copper(II) Ions

Abstract

The gemini surfactant sodium 4,8-dioctyl-3,9-dioxo-6-hydroxy-4,8-diaza-1,11-undecanedicarboxylate (SDUC), bearing two carboxylic headgroups and two hydrocarbon chains, has been synthesized, and its self-organization characteristics at strong basic and neutral environments have been studied. The results reveal that a transition from micelles to vesicles in SDUC aqueous solution occurs when the pH drops from 12.0 to 7.0. When a small amount of Cu(2+) ion is added to the SDUC solutions at both pH 12.0 and 7.0, remarkable transformations were observed within the SDUC aggregate structures. At pH 12.0, micelles transform into vesicles as Cu(2+) is added, while the vesicles of SDUC are formed at pH 7.0 and these small vesicles tend to fuse into larger ones slowly. Moreover, these SDUC vesicles at pH 7.0 undergo a relatively fast fission process when Cu(2+) is added in. An attempt has been made to explain the mechanism of these transformations.