Measurement of thin-film dissolution kinetics using a quartz crystal microbalance

A new general method for measuring the dissolution kinetics of thin films is described. In this technique, the film is cast on a piezoelectric quartz crystal. The mass of the dissolving film is determined as a function of time by monitoring the characteristic oscillation frequency of the crystal. Frequency shifts exhibited by the crystal are shown to be linearly related to the mass of the cast film. The method allows determination of the dissolution kinetics of films knowing only their density and the characteristic oscillation frequency of the uncoated quartz crystal. The technique has several advantages over alternative in situ methods based on optical interferometry or capacitance. It can be used to measure very high dissolution rates and to study thick or opaque films.