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

Atomistic molecular modeling techniques have proven to be a very useful tool for the investigation of the structure and dynamics of dense amorphous membrane polymers and of transport processes in these materials. As illustrations, the results of extensive atomistic molecular dynamics investigations on the transport of different small molecules in flexible chain rubbery and stiff chain glassy polymers are discussed. For this purpose bulk polymer models and interface models for liquid feed mixtures in contact 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 chain glassy polymers reveals qualitative differences which are decisive for experimentally observable differences in the diffusion of small molecules in these materials. The simulation results for the interface models reflect important features of experimentally well characterized pervaporation processes.