Effects of chain stiffness and salt concentration on responses of polyelectrolyte brushes under external electric field

Abstract

We report a molecular dynamics study on non-equilibrium dynamics of polyelectrolyte brushes under external electric fields. In this work, the effects of chain stiffness and salt concentration on static and dynamic responses of the brushes are addressed in detail. Our simulations indicate that varying these parameters induce rich electro-responsive behavior of the brushes. The increase of salt concentration results in the enhancement of an opposite electric field formed by non-equilibrium distribution of cations and anions, which resists stretching or shrinkage of grafted chains. At strong positive electric fields, the flexible brushes are more sensitive to the change of salt concentration. When reversing the electric field, the stiff brushes undergo a conformational transition from collapse to complete stretching. At high salt concentrations, dynamic responsive magnitude of the brush thickness to added electric field is strongly reduced. It was found that the fall time for the stiff brush becomes much shorter than that for the flexible brush. Additionally, increasing ion concentration leads to an excess extension or shrinkage of flexible brushes. For strongly stiff brushes, such phenomenon occurs in the presence or absence of salt.

Effect of Counterion Valence on Conformational Behavior of Spherical Polyelectrolyte Brushes Confined between Two Parallel Walls

“…The brushes adopt various conformational behavior depending on different oppositely charged components and their concentrations. Except for equilibrium brush conformations, molecular simulation works on the polyelectrolyte brushes in external fields, such as electric field [ 23 , 24 , 25 ], have been performed. The electric field can influence the fluid transport in channels coated with polyelectrolyte brushes through changing the conformations of the brushes.…”

Electroosmotic Flow in Mixed Polymer Brush-Grafted Nanochannels

“…Several groups have simulated the modulation of electroosmotic flow in polymer-coated channels using molecular dynamics methods [ 25 , 26 , 27 , 28 , 29 , 30 , 31 , 32 ], providing insights into the role of polymer coatings in controlling the EOF. Additionally, responsive behaviors of charged polymer brushes to the electric field normal to surfaces were also investigated through computer simulations [ 33 , 34 , 35 , 36 ].…”

Electro‐osmotic flow in nanochannels with voltage‐controlled polyelectrolyte brushes: Dependence on grafting density and normal electric field

“…Ouyang et al25 used molecular dynamics simulations to analyze the gating mechanisms in a polyelectrolyte‐grafted nanochannel under external electric field. Further, our group studied the effects of salt concentration and chain stiffness on response behavior of the brushes under added electric fields 26. These works revealed that polyelectrolyte brushes as the gating components show a strong static and dynamic response to the change of applied electric field.…”