Effect of Topology on the Statics and Dynamics of a Polymer Chain at the Fluid-Fluid Interface: A Molecular Dynamics Simulation Study

J Thongam and LS Shagolsem, LANGMUIR, 38, 6330-6342 (2022).

DOI: 10.1021/acs.langmuir.2c00210

The effect of chain topology on the statics and dynamics of a chain at the interface of two immiscible fluids is studied by means of molecular dynamic simulations. For three topologically different chains, namely, linear, ring, and trefoil-knot, of the 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 is investigated. For a sharp-interface binary-fluid system, the interface width is insensitive to both topology and polymer-fluid interaction nature, while a weak nonmonotonic variation is seen for a broad-interface system. Chain extension normal to the interface plane is significantly affected by the topology with a trefoil-knot chain, due to the additional constraint, which 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 the center-of-mass mean-square displacement (MSD) is independent of topology, i.e., all the chain types show the same diffusion exponent alpha (similar to 1). However, the self- diffusion constant depends on the topology and it is the largest for the trefoil-knot chain. An interesting observation pertaining to the early time behavior of monomeric MSD is that, within the subdiffusive 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 are related to the different chain conformation for the polymer- fluid interaction range below and above a threshold value equal to that of the self-interaction of the pure fluid phase.

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