A flexible polymer chain in a critical solvent: Coil or globule?

TL;DR

This study investigates how a flexible polymer chain behaves near a liquid-gas critical point in a solvent, revealing that interaction strength determines whether the polymer adopts a globular or expanded form, with implications for controlling polymer conformation.

Contribution

The paper introduces a self-consistent field theory approach to analyze polymer conformation near critical solvents, highlighting the impact of polymer-solvent interaction strength on chain state.

Findings

Weak interactions lead to globular polymer conformation

Strong interactions result in expanded polymer conformation

Critical solvent density fluctuations influence polymer shape

Abstract

We study the behavior of a flexible polymer chain in the presence of a low-molecular weight solvent in the vicinity of a liquid-gas critical point within the framework of a self-consistent field theory. The total free energy of the dilute polymer solution is expressed as a function of the radius of gyration of the polymer and the average solvent number density within the gyration volume at the level of the mean-field approximation. Varying the strength of attraction between polymer and solvent we show that two qualitatively different regimes occur at the liquid-gas critical point. In case of weak polymer-solvent interactions the polymer chain is in a globular state. On the contrary, in case of strong polymer-solvent interactions the polymer chain attains an expanded conformation. We discuss the influence of the critical solvent density fluctuations on the polymer conformation. The reported effect could be used to excert control on the polymer conformation by changing the thermodynamic state of the solvent. It could also be helpful to estimate the solvent density within the gyration volume of the polymer for drug delivery and molecular imprinting applications.