Redox-switched amphiphilic ionic liquid behavior in aqueous solution.

A new redox amphiphilic ionic liquid (AIL) containing ferrocene as a redox-active group was synthesized, 1-(11-ferrocenylundecyl)-3-methylimidazolium bromide (Fc11MIm+). Adsorption and aggregation of both reduced and oxidized forms of this ferrocenated AIL in aqueous solution were studied by surface tension measurements. The micellization was favored for the reduced ferrocenated AIL (Fc11MIm+) as compared with the oxidized ferrocenated AIL (Fc+11MIm+). Minimum areas at the air/aqueous solution interface were identical whereas limiting surface tensions were slightly different. This corroborated the formation of an expanded monolayer of redox active AIL at the interface. The electrochemical behavior of redox active AIL was investigated. The electrochemical responses of Fc11MIm+ aqueous solution interestingly differed, depending on its concentration. Below the cmc, the electrochemical reaction was dominated by ferrocenated AIL adsorbed onto the electrode surface; then above the cmc, it was controlled by the Fc11MIm+ diffusing to the electrode. For the latter, the electrochemical mechanism was suggested to couple with the disruption reaction of the reduced form micelles.