Poly(vinyl ferrocene) redox behavior in ionic liquids

We describe in this report a systematic electrochemical characterization of the ion-solvent coupling mechanisms of poly(vinyl ferrocene) (PVF) in pure ionic liquid (IL) and 0.1 M IL aqueous solutions. Our study showed that the unique solvation and ionic properties of ILs significantly affected the break-in process and the ion-solvent transport mechanisms of PVF redox switching. A square model that emphasized both faradaic and nonfaradaic processes of PVF was used to explain the unique irreversible break-in effect in the pure ILs. The electrochemical quartz crystal microbalance technique was used to characterize the PVF redox processes in 0.1 M 1-butyl-3-methyl imidazolium tetrafluoroborate and 0.1 M methanesulfonate ILs in which an obvious difference of cyclic voltammogram was observed. Our results suggested the existence of strong IL-polymer interaction in 0.1 M methanesulfonate IL solutions, i.e., not only the anions but also the IL molecules interacted with the PVF matrix. The cations were later removed from the PVF matrix to balance the excessive positive charge in PVF oxidation. Our study confirmed that IL was not only an electrolyte but also a solvent in PVF redox switching processes. Various types of interactions between PVF and the IL, including dispersion, dipole induction, dipole orientation, hydrogen-bonding, or ionic/charge-charge interactions, could significantly change the PVF redox dynamics. Thus, IL tremendous diversity in structural and chemical properties and their distinctive properties offer us an excellent opportunity to explore IL-polymer interactions and to dynamically control the conductive polymer relaxation processes and their redox switching mechanism for various applications. (C) 2008 The Electrochemical Society.