(645c) A Molecular Insight Into the Translocation Mechanism of Solvent Molecules In Amorphous Polymer Matrices

Diffusion of small molecules in glassy amorphous polymer is known to be dominated by the so-called "hopping" motion. Penetrant molecules are usually constrained in small cavities within the polymer matrix for extended periods of time, before sudden translocation from one cavity to another takes place. The time scale between consecutive hopping events can be a few nanoseconds or even longer for certain penetrant-polymer systems, limiting classical atomistic molecular dynamics simulations to few realizations of such pathways. We apply transition path sampling techniques to harvest a large number of these events, and systematically investigate their mechanism. Effects of penetrant-polymer interactions, as well as polymer chain configuration and its fluctuations, on the translocation process will be quantitatively examined. The goal is to obtain a molecular level insight into the mechanism of penetrant movements in a polymer matrix. This knowledge could provide theoretical guidelines in various applications, such as solvent selection in the coating of polymer films and design of polymer membranes for liquid or gas separations.