Efficient equilibration of confined and free-standing films of highly entangled polymer melts

TL;DR

This paper presents a new efficient simulation method for equilibrating highly entangled polymer melts in confined and free-standing films, combining coarse-grained modeling with backmapping to microscopic detail.

Contribution

It introduces a versatile approach that maintains bulk density and conformational properties in confined polymer melts, applicable to various film geometries and microscopic models.

Findings

Confined polymer melts reach bulk-like conformations under weak confinement.

The method efficiently equilibrates large polymer films of different thicknesses.

Backmapping preserves microscopic details after coarse-grained equilibration.

Abstract

Equilibration of polymer melts containing highly entangled long polymer chains in confinement or with free surfaces is a challenge for computer simulations. We approach this problem by first studying polymer melts based on the soft-sphere coarse-grained model confined between two walls with periodic boundary conditions in two directions parallel to the walls. Then we apply backmapping to reinsert the microscopic details of the underlying bead-spring model. Tuning the strength of the wall potential, the monomer density of confined polymer melts in equilibrium is kept at the bulk density even near the walls. In a weak confining regime, we observe the same conformational properties of chains as in the bulk melt showing that our confined polymer melts have reached their equilibrated state. Our methodology provides an efficient way of equilibrating large polymer films with different thicknesses and is not confined to a specific underlying microscopic model. Switching off the wall potential in the direction perpendicular to the walls, enables to study free-standing highly entangled polymer films or polymer films with one supporting substrate.