Electrochemical Control of the Interactions of Polymers and Redox-Active Surfactants

Abstract

We report the characterization of aqueous solutions (0.1 M Li(2)SO(4)) of dilute ethyl(hydroxyethyl) cellulose (EHEC) mixed with the redox-active surfactant (11-ferrocenylundecyl)trimethylammonium bromide (FTMA) by measurements of clouding temperatures and dynamic light scattering. The investigation sought to test the hypothesis that FTMA, which forms micelles in aqueous solution in its reduced state but not in its oxidized state, would permit reversible control over the formation of polymer-surfactant complexes in solution. Our measurements revealed that low concentrations of reduced FTMA enhance aggregation, whereas high concentrations of reduced FTMA disperse polymer-surfactant aggregates. This behavior is qualitatively similar to both dodecyltrimethylammonium bromide and sodium dodecyl sulfate and reflects cooperative interactions between FTMA and EHEC. In contrast, oxidized FTMA was found not to promote EHEC aggregation at low concentrations of oxidized FTMA nor disperse EHEC aggregates at high concentrations. Measurements of dynamic light scattering revealed that the reduction of oxidized FTMA in solutions of EHEC containing 0.1-0.3 mmolal FTMA causes an increase in the sizes of polymer-surfactant aggregates of more than 1 order of magnitude. Our cloud point measurements also revealed that clouding can be induced isothermally via the electrochemical reduction of oxidized FTMA at room temperature at FTMA concentrations between 0.4 and 10 mmolal. In contrast, at concentrations of FTMA greater than 15 mmolal, the reduction of oxidized FTMA induces the clearing of EHEC solutions. We conclude that aggregation of EHEC in dilute solutions can be controlled by the manipulation of the oxidation state of FTMA.