Infuence of surface characteristics on fast-aggregating protein-coated polymer colloids

A study of fast aggregating surface modified colloidal particles is presented. The surface characteristics of the particles were modified by adsorbing different amounts of bovine serum albumin. Since the protein charge depends on the electrochemical properties of the suspension medium, the influence of the protein net charge on both the cluster structure and the aggregation mechanisms could be studied by changing the pH of the aqueous phase. Physical parameters, such as the fractal dimension, the scaling exponent and the aggregation rate, were determined by laser light scattering. The experimental results show that the adsorbed protein molecules modify the aggregation mechanism and allow structural rearrangement within the clusters.These effects are more pronounced when the protein molecules bear net charge. Weak flocculation could not be detected, which means that steric stabilization is totally effective. Near the isoelectric point, coagulation and bridging flocculation are the predominant aggregation mechanisms and are diffusion-controlled. Bridging flocculation, however, becomes less effective at pH 9.