Polymer chain collapse induced by many-body dipole correlations

TL;DR

This paper develops an analytical theory for flexible polymers with permanent dipoles, showing how dipole correlations and dielectric heterogeneity influence coil collapse or expansion, and analyzing the coil-globule transition.

Contribution

It introduces a many-body analytical framework to understand how dipole correlations and dielectric effects drive polymer coil collapse or expansion.

Findings

Dipole correlations act as pairwise interactions in coil conformations.

Dielectric mismatch can cause polymer coil expansion or collapse depending on permittivity.

Higher-order dipole correlations smooth the coil-globule transition.

Abstract

We present a simple analytical theory of flexible polymer chain dissolved in a good solvent, carrying permanent freely oriented dipoles on the monomers. We take into account the dipole correlations within the random phase approximation (RPA), as well as a dielectric heterogeneity in the internal polymer volume relative to the bulk solution. We demonstrate that the dipole correlations of monomers can be taken into account as pairwise ones only when the polymer chain is in a coil conformation. In this case the dipole correlations manifest themselves through the Keesom interactions of the permanent dipoles. On the other hand, the dielectric heterogeneity effect (dielectric mismatch effect) leads to effective interaction between the monomers of the polymeric coil. Both of these effects can be taken into account by the renormalizing the second virial coefficient of the volume interactions monomer-monomer. We establish that in the case when the solvent dielectric permittivity exceeds the dielectric permittivity of the polymeric material, the dielectric mismatch effect competes with the dipole attractive interactions, leading to polymer coil expansion. In the opposite case, both the dielectric mismatch effect and the dipole attractive interaction lead to the polymer coil collapse. We analyse the coil-globule transition caused by the dipole correlations of monomers within the many-body theory. We demonstrate that accounting for the dipole correlations higher than pairwise ones smooths this pure electrostatics driven coil-globule transition of the polymer chain.