Unfolding Collapsed Polyelectrolytes in Alternating-Current Electric Fields

TL;DR

This study uses simulations and theory to show how AC electric fields can unfold collapsed polyelectrolytes by overcoming charge relaxation barriers, revealing the role of counterion dissociation in the process.

Contribution

It introduces a combined simulation and theoretical approach to understand polyelectrolyte unfolding under AC fields, highlighting the importance of counterion dissociation times.

Findings

AC fields can unfold collapsed chains when field strength exceeds DC threshold

Unfolding occurs below a critical frequency related to charge relaxation time

Counterion dissociation controls dipole formation and unfolding dynamics

Abstract

We investigate the unfolding of single polyelectrolyte (PE) chains collapsed by trivalent salt under the action of alternating-current (AC) electric fields through computer simulations and theoretical scaling. The results show that a collapsed chain can be unfolded by an AC field when the field strength exceeds the direct-current (DC) threshold and the frequency is below a critical value, corresponding to the inverse charge relaxation/dissociation time of condensed trivalent counterions at the interface of the collapsed electrolyte. This relaxation time is also shown to be identical to the DC chain fluctuation time, suggesting that the dissociation of condensed polyvalent counterion on the collapsed PE interface controls the polyelectrolyte dipole formation and unfolding dynamics under an AC electric field.