Heteropolymers in a Solvent at an Interface

TL;DR

This paper derives exact bounds for the free energy of heteropolymers at an interface, revealing localization and delocalization transitions depending on their hydrophobicity, applicable to various charge distributions.

Contribution

It provides the first rigorous bounds for heteropolymer free energy at an interface, including localization transition proofs for neutral polymers.

Findings

Neutral polymers are localized at any temperature.

Non-neutral polymers undergo a finite-temperature delocalization transition.

Results apply to both independent and correlated hydrophobic charges.

Abstract

Exact bounds are obtained for the quenched free energy of a polymer with random hydrophobicities in the presence of an interface separating a polar from a non polar solvent. The polymer may be ideal or have steric self-interactions. The bounds allow to prove that a ``neutral'' random polymer is localized near the interface at any temperature, whereas a ``non-neutral'' chain is shown to undergo a delocalization transition at a finite temperature. These results are valid for a quite general a priori probability distribution for both independent and correlated hydrophobic charges. As a particular case we consider random AB-copolymers and confirm recent numerical studies.