Coagulative nucleation and particle size distributions in emulsion polymerization

Abstract

A detailed theory is presented for nucleation kinetics in emulsion polymerization systems based on the coagulation of precursor particles (which may themselves be formed by either homogeneous nucleation or micellar entry). These precursor particles differ from true latex particles by a slower rate of polymerization and the lack of stability against coagulation. The coagulative nucleation theory combines extended Müller-Smoluchowski coagulation kinetics with DLVO theory. Expressions are provided for the time evolutions of the nucleation rate, particle number, and particle size distribution (PSD). With physically reasonable values for the parameters for the coagulation kinetics, agreement is obtained with data for styrene emulsion polymerization systems. In particular, excellent accord is obtained with the early-time evolution of the PSD, such data being especially sensitive to assumptions as to the nucleation mechanism. In addition, agreement is obtained with data on the dependence of particle number on surfactant and initiator concentrations.