Atomistic to coarse grained simulations of diffusion of small molecules into polymeric matrix

The diffusion of small molecules into a polymeric matrix often occurs on a wide range of length- and time-scales that are not easily accessible by standard atomistic simulations. It has limited applications of atomistic simulations for evaluating barrier properties of a polymeric film associated with the diffusion of small molecules into the film. Here, we present a multiscale scheme that combines atomistic and coarse-grained (CG) simulations for predicting the diffusion of small molecules into a polymeric film. The atomistic simulations are used to parameterize the CG MARTINI force field and to interpret time scales of the resulting CG models. As a case study, the developed scheme is applied to investigate the diffusion of the Octanal (C8) molecules into a polymeric film composed of four different components. Based on the atomistic simulations, the CG parameters for each polymer component in the film are optimized, and their ability to describe the mixed C8-polymer systems and predict the corresponding dynamic properties are tested. The diffusion results from the CG simulations are validated by analyzing effects of the concentration, the temperature, the water and the polymer components' weight ratio changes. It is shown that the CG simulations are much faster than the atomistic simulations and can describe the diffusion of C8 molecules into the polymeric film. This provides an effective way for studying the diffusion of small molecules into a complex polymeric matrix and evaluate its barrier properties.

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