The structure of aggregates formed during the very early stages of colloidal coagulation

Abstract

We report a Brownian dynamics simulation study of the effect of hydrodynamic and colloidal interactions on the structure of aggregates formed during the very early stages of coagulation of a dilute dispersion of spherical DLVO-type particles. Sets of trajectories have been computed for three types of Brownian encounters: monomer–dimer, monomer–trimer and dimer–dimer. Simulated structures of coagulated trimers and tetramers are compared with aggregate structures prior to coagulation. The presence of a significant secondary minimum in the colloidal potential leads to coagulated trimers and tetramers which are less compact than the flocculated aggregates, but more compact than coagulated aggregates formed in the absence of a significant secondary minimum. Introduction of interparticle hydrodynamic interactions has a small but discernible effect on the angular distribution of particles in coagulated trimers. For the same colloidal potential, coagulated tetramers made from monomer–trimer encounters are more compact than those made from dimer–dimer encounters. The simulation study has also been used to investigate the effect of interparticle interactions on the monomer–dimer coagulation rate constant and the time-dependent light-scattering intensity during the initial stages of coagulation.