Rod-like Polyelectrolyte Brushes with Mono- and Multivalent Counterions

TL;DR

This study uses Monte Carlo simulations to analyze how rod-like polyelectrolyte brushes behave with different counterions, revealing effects on brush height, conformation, and ordering.

Contribution

It introduces a model for rod-like polyelectrolyte brushes with monovalent and multivalent counterions, highlighting the impact of grafting density and counterion valency.

Findings

Brush height is insensitive to grafting density in certain regimes.

Multivalent counterions cause collapse and clustering of the brush.

Nematic order appears at high grafting densities, increasing brush height.

Abstract

A model of rod-like polyelectrolyte brushes in the presence of monovalent and multivalent counterions but with no added-salt is studied using Monte Carlo simulation. The average height of the brush, the histogram of rod conformations, and the counterion density profile are obtained for different values of the grafting density of the charge-neutral wall. For a domain of grafting densities, the brush height is found to be relatively insensitive to the density due to a competition between counterion condensation and inter-rod repulsion. In this regime, multivalent counterions collapse the brush in the form of linked clusters. Nematic order emerges at high grafting densities, resulting is an abrupt increase of the brush height.