Single chain properties of polyelectrolytes in poor solvent

TL;DR

This study uses molecular dynamics simulations to explore how strongly charged polyelectrolytes behave in poor solvents, revealing complex conformations like pearl-necklace structures influenced by charge, solvent quality, and counterions.

Contribution

It provides new insights into the conformational regimes of polyelectrolytes in poor solvents, especially regarding pearl-necklace structures and the effects of charge and counterion interactions.

Findings

Pearl-necklace structures form due to competition between hydrophobic and Coulomb interactions.

Large fluctuations in pearls and strings cause minimal changes in experimental form factors.

No first-order collapse into globules observed at counterion condensation.

Abstract

Using molecular dynamics simulations we study the behavior of a dilute solution of strongly charged polyelectrolytes in poor solvents, where we take counterions explicitly into account. We focus on the chain conformational properties under conditions where chain-chain interactions can be neglected, but the counterion concentration remains finite. We investigate the conformations with regard to the parameters chain length, Coulomb interaction strength, and solvent quality, and explore in which regime the competition between short range hydrophobic interactions and long range Coulomb interactions leads to pearl-necklace like structures. We observe that large number and size fluctuations in the pearls and strings lead to only small direct signatures in experimental observables like the single chain form factor. Furthermore we do not observe the predicted first order collapse of the necklace into a globular structure when counterion condensation sets in. We will also show that the pearl-necklace regime is rather small for strongly charged polyelectrolytes at finite densities. Even small changes in the charge fraction of the chain can have a large impact on the conformation due to the delicate interplay between counterion distribution and chain conformation.