Quartz microbalance studies of solvent and ion transport in thin polymer films in sensor applications of the QCM

The quartz crystal microbalance (QCM) has been applied to the study of mass changes within thin polymer films immobilized on the surface of the QCM. These studies have been in two contexts: (1) the determination of compositional changes within such thin films which have been subjected to electrochemical oxidation or reduction (i.e. injection or removal of charge), which necessarily causes ion transport to maintain electroneutrality and frequently causes solvent transport as well, and (2) the development of sensor elements capable of transducing chemical events, such as binding of an analyte to a host molecule immobilized within the thin film, into electrical signals. The focus is on the fundamental chemical and physical processes which can occur in such situations and their influence on the resonant frequency and conductance spectrum of the QCM/thin-film composite resonator. Also discussed is the use of the conductance spectrum as a diagnostic tool for the evaluation of changes in the viscoelastic properties of the thin film which might be induced, for example, by solvent incorporation into the film.<>