All-atom molecular dynamics simulation of solvent diffusion in a glassy polymer

The diffusion behavior of low molecular weight solvents in a glassy polymer significantly differs from Fickian diffusion and is known as Case II or Class II diffusion. In Case II diffusion, the major experimental observation is that a sharp concentration front moving at a constant speed separates a swollen, rubbery region from a glassy region of the polymer system. Observing Case II diffusion through simulation is very challenging mainly because of the computationally demanding nature of the diffusion process. We have designed a simulation approach to observe Case II type of diffusion in glassy polymers using all-atom simulation. In this presentation, we will share our recent atomistic molecular dynamics simulation results on the diffusion behavior of several low molecular weight solvents in a glassy polystyrene film. Accurate knowledge of the concentration profile of the solvent through the polymer film is crucial in determining the type of the diffusion process and will be the major focus of this presentation.