Polymer Conformations and Diffusion through a Monolayer of Confining Nanoparticles

EJ Bailey and RA Riggleman and KI Winey, MACROMOLECULES, 53, 8171-8180 (2020).

DOI: 10.1021/acs.macromol.0c01524

We present coarse-grained molecular dynamics simulations to probe chain- scale polymer conformations and diffusion between confining nanoparticles (NPs). By constructing a monolayer of hexagonally packed NPs in a polymer melt with athermal interactions, we observe the magnitude and length scale over which homogeneously confining NPs impact the polymer behavior, which provides fundamental insights into more complex polymer nanocomposites. We show that polymer conformations are more perturbed under strong confinement (i.e., when the interparticle distance, ID, is less than twice the polymer radius of gyration, 2R(g)) as compared to around an isolated NP, and the effect depends on the ratio of R-NP/R-g rather than either independently. In fact, these conformations can be quantitatively replicated by executing a simple random walk in a similarly confining environment. We also show that polymer diffusion is slowed by the presence of NPs, and the slowing persists far beyond the length scale over which polymer conformations are perturbed. Although the slowing is strongest similar to R-g from the NPs, the diffusion coefficient is slower even beyond similar to 5R(g) from the NPs. Furthermore, by analyzing the directional van Hove distributions, we show polymer diffusion away from the NP monolayer is bulk-like while diffusion through the monolayer is slower with increasing NP confinement. These molecular dynamics simulations provide fundamental insights into the temporal and spatial effect of confining, athermal NPs on chain-scale polymer conformations, and diffusion.

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