XPS study of counterion incorporation into poly(vinylferrocene)

XPS provides answers to two significant issues that arise in studying electroactive polymers. First, what fraction of possible charge centers participates in the redox process? Second, what are the relative partition coefficients of two counterions that compete as charge-compensating counterions? To answer both these questions, we emersed (or immersed) poly(vinylferrocene) films from (or into) supporting electrolytes while maintaining potential control to govern the electrochemical history of the electroactive film. We found that all ferrocene units in the surface of a poly(vinylferrocene) film deposited on gold can be oxidized when the counterion is perchlorate, tetrafluoroborate, hexafluorophosphate, tosylate, or 1,5-naphthalenedisulfonate. In answering the second question, no internal standard was needed: the concentration ratios of the two competing ions in both water and polymer phases were used as the experimental variables. For the completely oxidized ferricinium film, we found that the partition coefficient of perchlorate ions is 67% of that of fluoroborate ions.