Relative Chain Flexibility Determines the Spatial Arrangement and the Diffusion of a Single Ring Chain in Linear Chain Films

JH Choi and T Kwon and BJ Sung, MACROMOLECULES, 54, 11008-11018 (2021).

DOI: 10.1021/acs.macromol.1c01937

The flexibility of a single polymer chain, characterized by its persistence length, is considered to be an intrinsic property of the polymer chain, which determines its conformation and transport properties. In this work, we find from molecular dynamics simulations for a single ring polymer chain in thin films of linear chain melts that the relative flexibility of the ring chain (compared to the flexibility of linear chains) determines where the ring polymer chain is located within thin films and how fast the ring polymer chain diffuses laterally. In this work, we tune the flexibility of ring and linear chains by changing the bending angle potential parameter, while other intra- and intermolecular interaction potentials are identical for both ring and linear chains. We find that it is not the flexibility of individual polymer chains but the relative flexibility that determines the spatial arrangement of the ring chain in thin polymer films. When a ring polymer chain is more flexible (more rigid) than linear polymer chains, the ring polymer is more likely to be located at the film surface (the film center). Such spatial arrangement should originate from the conformational entropy of the ring polymer chain. The ring chain at the film surface is compressed more than that at the film center. This makes the ring chain at the surface threaded less by linear chains. Because the relatively flexible ring chain prefers the film surface (which is more mobile than at the film center) and experiences less entanglement, the relatively flexible ring chain diffuses faster than the relatively rigid ring chain.

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