Polymer Conformations and Dynamics under Confinement with Two Length Scales

Although many studies have analyzed the behavior of polymers under 1-D thin film and 2-D cylindrical confinement, the knowledge about how confinement geometries with more than one length scale, such as random porous networks, impact polymers is yet to be fully explored. We simulate both entangled and unentangled polymer melts confined in a diamond network geometry with two characteristic length scales, where polymers are likely to inhabit multiple interconnected and neighboring channels. In all the confined systems with entangled polymer chains, the polymer radius of gyration and the number of polymer entanglements per chain are reduced compared to the bulk. We analyze the chain relaxation based on Rouse modes and show separate, competing effects between the local friction near the wall and chain disentanglement. The disentanglement of confined polymers increases diffusivity of entangled polymers along confined channels compared to the bulk after the confined diffusivities are corrected for the tortuosity of the confinement. We anticipate that the corrections due to tortuosity could be important for properly characterizing the dynamics in complex geometries, including highly loaded nanocomposites.