Structure of charged colloid-polymer mixtures

We use a light scattering technique to investigate the effect of adding non-adsorbing charged polymers to a very dilute electrostatically stabilized colloidal suspension at low electrolyte concentration. The experimental results show that, as the polymer concentration increases, the main peak of the colloid-colloid structure factor moves to higher q-values, which cannot be only due to the screening of the direct colloid-colloid electrostatic repulsion. We show that the colloid-polymer electrostatic repulsions lead to enhanced depletion forces that have a strong influence on the colloid structure, even for diluted suspensions. The experimental results are interpreted using the off-lattice Polymer Reference Interaction Site Model (PRISM), and very good agreement is found for all polymer concentrations