(556b) Solvent Diffusion and Drying Properties of Amorphous Polymers Via Molecular Simulation

Continuous manufacturing of polymer films requires the efficient removal of solvent contents: enhanced drying performance is one of the major considerations in selecting the film formulation. The total drying time is often dominated by the final stage of drying where a small amount of moisture needs to diffuse through a film of mostly solid components. In this presentation we will first discuss the fundamental mechanism of solvent diffusion at this concentration regime. Diffusion of small molecules in amorphous polymers is known to follow a form of so-called hopping motion: penetrant molecules are trapped in microscopic cavities for extended time periods, and diffusion is made possible by rare but fast jumps between neighboring cavities. We study the molecular mechanism of these hopping motions by statistically analyzing the transitional path ensembles associated with individual hopping events. Our investigation shows that a hopping event starts when the solvent molecule is able to (1) find a pathway between cavities that it is able to push open and (2) break the hydrogen bonds it has formed with the polymer matrix in the original cavity. We then quantify the structural features of polymer matrices that are important to the solvent diffusion according to this mechanism. These quantities are evaluated for different polymer formulations, and their capability of predicting the drying properties is tested through comparison with experimental drying curves. These investigations will provide guidelines for the formulation design of polymer film casting.