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

Lujuan Li,Qianqian Cao,Chuncheng Zuo

doi:10.3390/polym10040363

Abstract

We study the conformational behavior of spherical polyelectrolyte brushes in the presence of monovalent and trivalent counterions in a confined environment. The confinement is exerted by two parallel walls on the brushes. The enhancement of the confinement induces the extension of grafted chains. For the monovalent case, the increase of the charge fraction leads to extended brush conformation for different slit width (distance between two walls) but collapsed brush in the presence of trivalent counterions is observed. The confinement does not affect electrostatic correlation between trivalent counterions and charged monomers. However, it was found that narrow slit width contributes to stronger electrostatic correlation for the monovalent case. This is because more monovalent counterions are inside the brush at strong confinement, but almost all trivalent counterions are trapped into the brush independently of the slit width. The diffusion of counterions under the confinement is related to the electrostatic correlation. Our simulations also reveal that the brush thickness depends on the slit width nonlinearly.

Highlights

When polyelectrolyte chains are grafted densely on a substrate surface, known polyelectrolyte brushes, the brushes exhibit rich conformational behavior due to the long-range electrostatic interaction [1,2,3,4]
In this work, based on molecular dynamics simulations we investigated conformational behavior of the SPB in the presence of monovalent and trivalent counterions in a confined environment
The brush thickness depends on the slit width nonlinearly and reaches minimum at intermediate slit width

Summary

Introduction

When polyelectrolyte chains are grafted densely on a substrate surface, known polyelectrolyte brushes, the brushes exhibit rich conformational behavior due to the long-range electrostatic interaction [1,2,3,4]. To obtain an insight into the structures and dynamics of these systems, theoretical studies of polyelectrolyte brushes in solution based on self-consistent field theories [5,6,7] and scaling laws [8,9,10] were performed. Other methods, such as molecular theories [11,12,13], including more chain structure details, can provide more accurate results.

Simulation Model and Method

Brush Conformation

Electrostatic Correlation and Counterion Diffusion

Conclusions