THERMOPHYSICAL PROPERTIES OF PENETRANTS IN POLYMERS VIA A PIEZOELECTRIC QUARTZ-CRYSTAL MICROBALANCE

Accurate values for the equilibrium sorption and the diffusion rates o f penetrants in polymers are required for many important polymer produ ction and processing operations. This paper demonstrates the use of th e quartz crystal microbalance (QCM) as a means to readily produce diff usivity and equilibrium data. The QCM exploits the well-known piezoele ctric effect in quartz crystals to measure the mass sorption of a pene trant onto a polymer film. Nanogram resolution of the penetrant mass r esults in extreme accuracy. The mass sorbed as a function of time prov ides the necessary information to calculate the diffusion coefficient of the penetrant in the polymer, and the equilibrium mass provides the penetrant solubility. The flexibility and accuracy of the QCM are dem onstrated by examining several sets of data. A comparison of penetrant -diffusion data obtained from two different techniques (the QCM and gr avimetric sorption via a quartz spring balance) is presented to demons trate the accuracy of the QCM. The results from an industrial coating/ penetrant system are also given to demonstrate the capacity of the QCM to measure the equilibrium state.