DIFFUSION IN GLASSY POLYMER MEMBRANE CONSIDERING TIME DEPENDENCE OF SURFACE CONCENTRATION

Abstract

The uncertainty of the diffusion coefficient (D_θ) of glassy polymer film determined by the time-lag method (D_θ=l²/6θ), can be attributed to the relaxational behavior characteristic of glassy polymers. For glassy polymers, a surface concentration at one face of membrane is initially zero and reaches an equilibrium concentration exponentially. Fick's second law was solved under the boundary condition considering the time dependence of surface concentration and initial condition. Then, we obtained the total amount of penetrant diffusing through the membrane in time t. As t → ∞, this equation converges on the straight line. This line has an intercept on a t axis, which expresses the time-lag as a function of α(=βl²/D) indicating the time dependence of surface concentration. The time-lag method for the glassy polymer membrane was examined for different gases and different glassy polymers by using the equation obtained.