NUCLEATION MECHANISMS AND PARTICLE-SIZE DISTRIBUTIONS OF POLYMER COLLOIDS

A theoretical model is developed for the time evolution of volume particle size distributions (PSDs) of polymer colloids during the nucleation stage. Analytic expressions for the PSD and related cumulants are presented. Negatively skewed distributions are observed only when the formation rate of mature latex particles is a monotonically decreasing function of time. When this model is tested against experimental PSD data of styrene polymerization at 50-degrees-C, agreement between theory and experiment is found only assuming a monotonically decreasing nucleation rate. The fitting is completely missed when the production rate of mature latex particles is predicted according to the coagulative nucleation scheme. Theory and experiment can combine introducing an extended coagulative nucleation model. According to this approach, the nucleation time is much shorter than predicted by earlier theories. As a consequence, most of the mechanistic information convoluted with early-time PSDs is lost.