Abstract
We apply a hierarchy of multiscale modeling approaches to investigate the structure of ring polymer solutions under planar confinement. In particular, we employ both monomer-resolved (MR-DFT) and a coarse-grained (CG-DFT) density functional theories for fully flexible ring polymers, with the former based on a flexible tangent hard-sphere model and the latter based on an effective soft-colloid representation, to elucidate the ring polymer organization within slits of variable width in different concentration regimes. The predicted monomer and polymer center-of-mass densities in confinement, as well as the surface tension at the solution-wall interface, are compared to explicit molecular dynamics (MD) simulations. The approaches yield quantitative (MR-DFT) or semiquantitative (CG-DFT) agreement with MD. In addition, we provide a systematic comparison between confined linear and ring polymer solutions. When compared to their linear counterparts, the rings are found to feature a higher propensity to structure in confinement that translates into a distinct shape of the depletion potentials between two walls immersed into a polymer solution. The depletion potentials that we extract from CG-DFT and MR-DFT are in semiquantitative agreement with each other. Overall, we find consistency among all approaches as regards the shapes, trends, and qualitative characteristics of density profiles and depletion potentials induced on hard walls by linear and cyclic polymers.
Highlights
Topological effects can have a profound impact on static and dynamic properties of polymers, being especially pronounced in melts and solutions of polymer rings
Some discrepancy in the surface tension results is observed at higher densities, which might be attributed to the approximations employed in the equation of state (EOS)
CG-density functional theory (DFT) provides a good description for the structure of ring polymer solutions within slits of variable width up to ρp/ρp* ≲ 0.6−0.8 (Figure 6), despite polymer deformations in the vicinity of the walls found in molecular dynamics (MD) (Figure 2)
Summary
Topological effects can have a profound impact on static and dynamic properties of polymers, being especially pronounced in melts and solutions of polymer rings. Many thermodynamics properties of ring polymer solutions in the dilute regime can be described using the effective representation of polymer coils as “soft colloids” interacting via effective potentials Veff(r).[29] For instance, in our previous work,[19] it was shown using a mean-field density functional theory (DFT) that the distinct form of Veff(r) for rings leads to a stronger tendency of rings to structure in planar confinement in comparison to the linear counterparts. The latter approach will be denoted as the coarse-grained DFT (CG-DFT) throughout this work. We compare the polymerinduced depletion potentials as obtained from CG-DFT and MR-DFT, and we find good agreement between the two at comparable densities in the dilute regime, indicating rings as stronger depletants as compared to linear chains at similar volume fractions of the polymer component
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