Detailed-atomistic molecular modeling of small molecule diffusion and solution processes in polymeric membrane materials

Feature Article: Atomistic molecular modeling techniques have proven to be a very useful tool for the investigation of the structure and dynamics of d ense amorphous membrane polymers and of transport processes in these materi als. As illustrations, the results of extensive atomistic molecular dynamic s investigations on the transport of different small molecules in flexible chain rubbery and stiff chain glassy polymers are discussed. For this purpo se bulk polymer models and interface models for liquid feed mixtures in con tract with the upstream site of the respective membrane have been employed. A comparison between the static structure and the dynamic behavior of the free volume in the simulated flexible chain rubbery polymers and stiff chai n glassy polymers reveals qualitative differences which are decisive for ex perimentally observable differences in the diffusion of small molecules in these materials. The simulation results for the interface models reflect im portant features of experimentally well characterized pervaporation process es.