Effect of topology on the statics and dynamics of a polymer chain at the fluid-fluid interface: a molecular dynamics simulation study

TL;DR

This study uses molecular dynamics simulations to explore how different chain topologies (linear, ring, trefoil-knot) influence the static and dynamic behavior of polymers at fluid-fluid interfaces, revealing topology-dependent conformations and diffusion properties.

Contribution

It provides new insights into the impact of chain topology on polymer interface behavior, highlighting effects on chain extension, shape, and diffusion that were previously not well understood.

Findings

Interface width is insensitive to topology in sharp-interface systems.

Trefoil-knot chains have the largest extension normal to the interface.

Self-diffusion constant varies with topology, highest for trefoil-knot.

Abstract

The effect of chain topology on the statics and dynamics of chain at the interface of two immiscible fluids is studied by means of molecular dynamics simulations. For three topologically different chains, namely, linear, ring, and trefoil-knot of same molecular weight the effect of varying both polymer--fluid and fluid--fluid interaction nature on the width of the fluid interface, chain conformation, shape, and chain dynamics. For sharp-interface binary-fluid system, the interface width is insensitive to both topology and polymer-fluid interaction nature, while a weak non-monotonic variation is seen for weak-interface system. Chain extension normal to the interface plane is significantly affected by the topology with trefoil-knot chain, due to the additional constraint, has the largest value compared to both linear and ring polymers. Instantaneous shapes are also quantified through shape parameters. Furthermore, it is observed that the qualitative behavior of center of mass mean-square displacement (MSD) is independent of topology, i.e., all the chain types show same diffusion exponent $\alpha~(\approx 1)$. However, the self-diffusion constant depends on the topology and it is largest for trefoil-knot chain. An interesting observation pertaining the early time behavior of monomeric-MSD is that, within the sub-diffusive regime, the values of $\alpha$ for different parameters (independent of topology) are grouped into two distinct ranges (0.52--0.59 and 0.62--0.67) which is related to the different chain conformation for polymer-fluid interaction range below and above a threshold value equal to that of the self-interaction of the pure fluid phase.