Electrosteric stabilization of colloidal dispersions

The electrosteric stabilization of model colloidal dispersions is quantified through high-frequency rheometry and complementary techniques. Model aqueous dispersions with a poly(butyl acrylate)polystyrene core and a layer of poly(methacrylic acid) grafted onto the surface are prepared and characterized. The influence of pH, electrolyte concentration, and amount of polymer in the stabilizing layer on dispersion stability and rheology is investigated. Dynamic light scattering, electrophoretic mobility, and rheology are used to quantify thickness, hydrodynamic permeability, and charge density of the stabilizing shell. A collapsed layer at low pH leads to aggregation after addition of salt, while a swollen layer at high pH induces stability. The colloidal interaction potential is deduced from measurements of the high-frequency elastic modulus using torsional resonators. The complex electrosteric forces are shown to be dominated by the excess osmotic pressure created by overlap of the electrosteric layer for particles in contact. The measured moduli G'(infinity) can be predicted quantitatively based on a simple model for the osmotic repulsion introduced by Vincent et al. [J. Colloid Interface Sci. 1986, 18, 261] without adjustable parameters.