Theoretical and Experimental Adsorption Studies of Polyelectrolytes on an Oppositely Charged Surface

TL;DR

This study combines experimental and simulation approaches to investigate the electrostatic interactions and adhesion forces between charged polyelectrolytes and oppositely charged surfaces, revealing weak salt dependence and structural stability.

Contribution

It provides a comprehensive analysis of polyelectrolyte-surface interactions through combined theoretical, simulation, and experimental methods, highlighting the weak influence of salt concentration.

Findings

Adhesion force is weakly dependent on salt concentration.

Polymer monolayer structure remains stable across different ionic strengths.

Simulation results agree with Debye-Huckel approximation near 0.1 M salt.

Abstract

Using self-assembly techniques, x-ray reflectivity measurements, and computer simulations, we study the effective interaction between charged polymer rods and surfaces. Long-time Brownian dynamics simulations are used to measure the effective adhesion force acting on the rods in a model consisting of a planar array of uniformly positively charged, stiff rods and a negatively charged planar substrate in the presence of explicit monovalent counterions and added monovalent salt ions in a continuous, isotropic dielectric medium. This electrostatic model predicts an attractive polymer-surface adhesion force that is weakly dependent on the bulk salt concentration and that shows fair agreement with a Debye-Huckel approximation for the macroion interaction at salt concentrations near 0.1 M. Complementary x-ray reflectivity experiments on poly(diallyldimethyl ammonium) chloride (PDDA) monolayer films on the native oxide of silicon show that monolayer structure, electron density, and surface roughness are likewise independent of the bulk ionic strength of the solution.