Brownian Dynamics Simulation of the Capture of Primary Radicals in Dispersions of Colloidal Polymer Particles

The kinetics of collision between primary persulfate radicals and colloidal polymer particles, a key issue in emulsion polymerization modeling, is determined by the simulation of Brownian dynamics using a Monte Carlo random flight algorithm. The results obtained confirm the ideal behavior predicted by Smoluchowski's kinetic equation only in colloidal dispersions of very low polymer volume fractions (<0.1%), while at higher values, significant deviations from ideality are observed. This deviation from ideality, designated as the Smoluchowski number (Sm), is found to increase almost linearly with the volume fraction of the dispersion. The kinetic model considering the effect of volume fraction is compared with previous experimental data. A satisfactory explanation for the different functional dependences of the radical entry rate on particle diameter is obtained. It is concluded that the polymer volume fraction in the dispersion plays a major role in the mechanism of radical capture by polymer particles.