Interactions between Surfaces Mediated By Polyelectrolyte Dispersants

Polymer dispersants are commonly used to obtain homogenous dispersions of colloids in the liquid phase. Dispersants impart stability to a colloidal solution by creating a steric and/or electrostatic barrier on close approach of two colloids. While polyelectrolytes are used extensively as dispersants, the underlying physics guiding the induced repulsion are not fully understood. Prediction of the polymer-mediated repulsion requires accurate description of the complex interplay between chain connectivity, excluded volume, and electrostatics. We demonstrate that both liquid state theory and self-consistent field theory aptly predict regimes of colloidal stability, flocculation, and agglomeration for polyelectrolyte dispersants. In particular, we show that sufficient strength of non-electrostatic adsorption is required for stabilization. We also study how the solution pH, salt content, and polymer architecture impact both the adsorption of polymer to the colloid surface and the induced repulsion between colloidal particles.