# Residual entropy in a model for the unfolding of single polymer chains

## TL;DR

This paper investigates the unfolding process of flexible single polymer chains under external force using a simplified model that reveals residual entropy and reentrant phase behavior, with all calculations performed in closed form.

## Contribution

It introduces a novel simplified model for polymer unfolding that does not rely on Boltzmann-Gibbs assumptions and explicitly demonstrates residual entropy effects.

## Key findings

- Gradual globule-to-rod transition observed.
- Reentrant boundary line between phases due to residual entropy.
- Model allows closed-form calculations without standard equilibrium assumptions.

## Abstract

We study the unfolding of a single polymer chain due to an external force. We use a simplified model which allows to perform all calculations in closed form without assuming a Boltzmann-Gibbs form for the equilibrium distribution. Temperature is then defined by calculating the Legendre transform of the entropy under certain constraints. The application of the model is limited to flexible polymers. It exhibits a gradual transition from compact globule to rod. The boundary line between these two phases shows reentrant behavior. This behavior is explained by the presence of residual entropy.