Pulsed ion beam technique for measuring diffusion coefficient of a slow diffusant in polymers

Abstract

The determination of diffusion coefficients (D) of small molecules in a polymer for D below 10−10 cm2 s−1 is a difficult measurement using conventional self-supporting polymer membrane techniques. We propose a new method for obtaining similar information by irradiating a polymer with a pulsed ion beam and studying the evolving gaseous products. Product molecules that are not limited by the rate of their production in the film tend to exhibit diffusion limited dynamical characteristics in their transient evolution from the surface. By numerically modeling the diffusion problem we can extract diffusion coefficients from the data. Since thin films (<1 μm) can be used in these experiments, diffusion coefficients less than 10−10 cm2 s−1, typical of many molecules in polymers, can be measured with ease.