Free energy of self-avoiding polymer chain confined between parallel walls

TL;DR

This paper introduces a novel empirical method to compute the free energy and entropic forces of self-avoiding polymer chains confined between parallel walls, overcoming limitations of traditional simulation techniques.

Contribution

It proposes an innovative approach using force measurements with an elastic spring to interpolate the free energy of confined polymers, extending classical theories.

Findings

Derived an analytical expression for confined self-avoiding chain free energy.

Validated the method through comparison with classical ideal chain theory.

The approach can be applied to various confinement scenarios.

Abstract

Understanding and computing the entropic forces exerted by polymer chains under confinement is important for many reasons, from research to applications. However, extracting properties related to the free energy, such as the force (or pressure) on confining walls, does not readily emerge from conventional polymer dynamics simulations due to the entropic contributions inherent in these free energies. Here we propose an alternative method to compute such forces, and the associated free energies, based on empirically measuring the average force required to confine a polymer chain between parallel walls connected by an artificial elastic spring. This measurement enables us to interpolate the expression for the free energy of a confined self-avoiding chain and offer an analytical expression to complement the classical theory of ideal chains in confined spaces. Therefore, the significance of our method extends beyond the findings of this paper: it can be effectively employed to investigate the confinement free energy across diverse scenarios where all kinds of polymer chains are confined in a gap between parallel walls.