Abstract
This work is concerned with the diffusivity in polymeric two-component systems in which the penetrant concentration is infinitely dilute. In polymeric systems the Wilke-Chang equation does not hold, and diffusivity shows an anomalous behavior; that is, it shows a constant value regardless of medium molecular weight. This anomaly is accounted for in this work.
The diffusivity of non-polymeric and polymeric molecules through a polymeric medium has been derived theoretically as an extension of the free-volume theory by Bueche. With this formulation, a simple expression has been developed to correlate diffusivity, viscosity, temperature and molecular weight of the system. Good agreement with the experimental data for the polydimethylsiloxane system is obtained. It is found that Dη/T is proportional to M3.5 for the range of M>Mb, and to M for the range of M<Mb, where M is the molecular weight of polymeric medium and Mb, is a characteristic value.
