Response of the Polyelectrolyte Brushes to External Electric Field and the Associated Flow Modifications: An Atomistic Perspective

Polyelectrolyte (PE) brushes are of great importance in countless applications due to their diverse responses to environmental stimuli. Here, we study the effect of external fields on PE brushes using all-atoms molecular dynamics simulations. Our simulations showed that the external axial electric field can reduce the height of the PE brushes significantly. Depending on the charge distribution of their pendant groups, the PE brushes respond to the external electric field in two different ways. When the charge density is high and the counterions are strongly attached to the oppositely charged monomers, the asymmetry in the distribution of the counterions leads to a reduction in the brush height. On the other hand, when the charge density is small and the counterions are not bound to the monomers tightly, the PE brush can tilt in response to the electric field lowering the brush height. We have also discovered that the axial electric field in a PE brush-grafted nanochannel can control the overscreening behavior (inside the PE brush layer), co-ion dominated electroosmotic (EOS) flow and field strength dependent reversal in the EOS flow directions. Finally, this overscreening behavior can lead to simultaneous power generation and flow enhancement under an applied pressure gradient.