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 insert 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.
Highlights
Polymer confinement plays an important role for many aspects of adhesion, wetting, lubrication, and friction of complex fluids from both theoretical and technological points of view
It is important to understand the mechanical properties of confined polymer melts and how confinement impacts both viscous and elastic properties of amorphous polymer films with different surface substrates or even free surfaces
We have developed an efficient methodology to equilibrate long chain polymer films and applied this method to a polymer film where 1000 chains of 2000 ≈ 72Ne monomers are confined between two repulsive walls at the bulk melt density ρ = 0.85σ−3
Summary
Polymer confinement plays an important role for many aspects of adhesion, wetting, lubrication, and friction of complex fluids from both theoretical and technological points of view. One of the successful monomer-based models, namely, the bead-spring (BS) model together with an additional bond-bending potential, has been successfully employed to provide a better understanding of generic scaling properties of polymer melts in bulk. For such a model, static and dynamic properties of highly entangled polymer melts in bulk have been extensively studied in our previous work.. Through a hierarchical backmapping of CG chains described by the soft-sphere CG model from low resolution to high resolution and a reinserting of microscopic details of bead-spring chains, highly entangled polymer melts in bulk are equilibrated by molecular dynamics (MD) simulations using the package ESPResSO++.44,45.
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