Knotting behaviour of polymer chains in the melt state for soft-core models with and without slip-springs

Zhenghao Wu,Jurek Schneider,Florian Müller-Plathe,Simon A N Alberti

doi:10.1088/1361-648x/abef25

Abstract

We analyse the knotting behaviour of linear polymer melts in two types of soft-core models, namely dissipative-particle dynamics and hybrid-particle-field models, as well as their variants with slip-springs which are added to recover entangled polymer dynamics. The probability to form knots is found drastically higher in the hybrid-particle-field model compared to its parent hard-core molecular dynamics model. By comparing the knottedness in dissipative-particle dynamics and hybrid-particle-field models with and without slip-springs, we find the impact of slip-springs on the knotting properties to be negligible. As a dynamic property, we measure the characteristic time of knot formation and destruction, and find it to be (i) of the same order as single-monomer motion and (ii) independent of the chain length in all soft-core models. Knots are therefore formed and destroyed predominantly by the unphysical chain crossing. This work demonstrates that the addition of slip-springs does not alter the knotting behaviour, and it provides a general understanding of knotted structures in these two soft-core models of polymer melts.

Highlights

We analyse the knotting behaviour of linear polymer melts in two types of soft-core models, namely dissipative-particle dynamics and hybrid-particle-field models, as well as their variants with slip-springs which are added to recover entangled polymer dynamics
By comparing the knottedness in dissipative-particle dynamics and hybrid-particle-field models with and without slip-springs, we find the impact of slip-springs on the knotting properties to be negligible
We discuss the differences in the knotting behaviour of our hard-core standard molecular dynamics (MD) model and the softcore hPF model derived from it

Summary

Introduction

There has been a considerable activity in the development and use of soft-core polymer models, i.e., models where the nonbonded interactions between monomers do not approach a singularity at short intermonomer distances, but assume a finite. The value is low enough, say of the order of 10 kBT (kB being Boltzmann’s constant), so that it does not even present ‘practical infinity’ in a simulation. Such models are engineered to reproduce static structural and thermodynamic properties of hard-core excluded-volume models as well as possible, with little attention given so far to their ability or disability to capture the propensity for polymer chains to form knots.

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