A Quantitative Theory of Mechanical Unfolding of a Homopolymer Globule

TL;DR

This paper develops a mean-field theory to describe how long homopolymer globules unfold under mechanical force, revealing different unfolding modes depending on chain length and solvent quality, and compares predictions with numerical simulations.

Contribution

It introduces a quantitative mean-field model for the mechanical unfolding of homopolymer globules, including phase diagrams and force-extension behavior, advancing understanding beyond prior qualitative approaches.

Findings

Unfolding can be continuous or involve micro-phase coexistence.

Force-extension curves are quantitatively predicted and matched with simulations.

Phase diagrams delineate one- and two-phase regions for different conditions.

Abstract

We propose the quantitative mean-field theory of mechanical unfolding of a globule formed by long flexible homopolymer chain collapsed in poor solvent and subjected to extensional deformation. We demonstrate that depending on the degree of polymerization and solvent quality (quantified by the Flory-Huggins $\chi$ parameter) the mechanical unfolding of the collapsed chain may either occur continuously (by passing a sequence of uniformly elongated configurations) or involves intra-molecular micro-phase coexistence of a collapsed and a stretched segment followed by an abrupt unraveling transition. The force-extension curves are obtained and quantitatively compared to our recent results of numerical self-consistent field (SCF) simulations. The phase diagrams for extended homopolymer chains in poor solvent comprising one- and two-phase regions are calculated for different chain length or/and solvent quality.