Computational models for multicomponent diffusion in polymeric materials

Situations where a polymeric material is exposed to a solvent mixture so that the different components within the mixture can diffuse into the polymer are common both in industrial applications and in biological processes. Often one of the components is taken up preferentially and its presence affects the diffusion properties of the remaining components. The problem of accounting for processes of this type has not been dealt with in a systematic way. This may in part be due to the difficulty of characterizing experimentally the separate diffusion behavior of the various components: data of this kind are now becoming available for simple binary mixtures. In order to model this class of problems, a lattice model involving a polymer matrix (M) and two diffusing components (A and B) has been introduced. The Monte Carlo evolution of the system has been examined for different values of the local A-M, B-M and A-B interactions. These results shed light on the microscopic origin of selective uptake.