Inverse swelling of a hydrophobic polymer in aqueous solution

TL;DR

This paper models the inverse swelling of hydrophobic polymers in water, showing how temperature and pressure influence swelling transitions using a lattice-fluid approach.

Contribution

It introduces a lattice-fluid model for inverse polymer swelling, capturing first and second order transitions based on interaction parameters.

Findings

Model exhibits first and second order swelling transitions.

Swelling behavior depends on temperature, pressure, and interaction parameters.

The approach links hydrophobicity to thermodynamic anomalies in water.

Abstract

We address the problem of inverse polymer swelling. This phenomenon, in which a collapsed polymer chain swells upon decreasing temperature, can be observed experimentally in so-called thermoreversible homopolymers in aqueous solution, and is believed to be related to the role of hydrophobicity in protein folding. We consider a lattice-fluid model of water, defined on a body-centered cubic lattice, which has been previously shown to account for most thermodynamic anomalies of water and of hydrophobic solvation for monomeric solutes. We represent the polymer as a self-avoiding walk on the same lattice, and investigate the resulting model at a first order approximation level, equivalent to the exact calculation on a Husimi lattice. Depending on interaction parameters and applied pressure, the model exhibits first and/or second order swelling transitions upon decreasing temperature.