Strongly Charged Polymer Brushes

TL;DR

This paper develops phase diagrams for strongly charged polymer brushes, revealing electrostatic stiffening, counterion condensation, and specific scaling laws for brush height with salt concentration, aligning well with experimental data.

Contribution

It introduces a theoretical framework for strongly charged brushes, incorporating effects absent in weakly charged models, and derives new scaling laws for brush height.

Findings

Brush height scales as n_s^(-1/3) at high salt concentrations

Electrostatic stiffening influences chain conformation

Counterion condensation affects brush behavior

Abstract

Charged polymer brushes are layers of surface-tethered chains. Experimental systems are frequently strongly charged. Here we calculate phase diagrams for such brushes in terms of salt concentration n_s, grafting density and polymer backbone charge density. Electrostatic stiffening and counterion condensation effects arise which are absent from weakly charged brushes. In various phases chains are locally or globally fully stretched and brush height H has unique scaling forms; at higher salt concentrations we find H ~ n_s^(-1/3), in good agreement with experiment.