GROWTH OF COLLOIDAL AGGREGATES THROUGH POLYMER BRIDGING

The stability of colloidal dispersions can be altered through the addition of adsorbing macromolecules. Adsorption of macromolecules on the particle surfaces results in a stepwise aggregation process. We consider the early destabilization steps for nanometric ceria particles dispersed in water. These steps have been characterized through light scattering; they are: i) finite multiplets involving one macromolecule and a small number of particles; ii) bridging between multiplets; iii) formation of three-dimensional networks of bridges. Each stage can be obtained as an equilibrium state, provided there is an adequate balance of electrostatic repulsions and polymer-induced attractions. Altering this balance may push the system from one state into another, or it may change the structure within one state. For instance, multiplets may be pushed to bind more particles or spill them out, depending on the equilibrium length of bridges; gels may reject solvent and turn into flocs if the equilibrium length of bridges becomes shorter than the average distance between particles.