Ion Correlation-Driven Hysteretic Adhesion and Repulsion between Opposing Polyelectrolyte Brushes

TL;DR

This study uses an advanced theoretical model to reveal how ion correlations cause hysteresis, adhesion, and repulsion in opposing polyelectrolyte brushes, aligning well with experimental observations.

Contribution

It introduces a self-consistent field theory incorporating ion correlations to explain hysteretic forces and specific ion effects in polyelectrolyte brush interactions.

Findings

Ion correlations induce hysteretic normal stress in PE brushes.

Force profile shows discontinuity with trivalent ions, indicating adhesion and repulsion.

The theory matches experimental results on ion-specific effects.

Abstract

Polyelectrolyte (PE) brushes are widely used in biomaterials and nanotechnology to regulate surface properties and interactions. Here, we apply the electrostatic correlation augmented self-consistent field theory to investigate the interactions between opposing PE brushes in a mixture of 1:1 and 3:1 salt solutions. Our theory predicts hysteretic feature of the normal stress induced by strong ion correlations. In the presence of trivalent ions, the force profile is discontinuous: repulsive in the compression branch and adhesive in the separation branch. The molecular origin of the hysteretic force is the coexistence of two collapsed modes: two separated condensed layer on each surface in the compression and a single bundled condensed layer in the separation. With the systematic inclusion of ion correlations, our theory fully captures the hysteretic force, adhesive separation, ``jump-in'' and ``jump-out'' features, and the ``specific ion effect'', all in good agreement with the reported experimental results.