Direct Visualization of Coagulative Nucleation in Surfactant-Free Emulsion Polymerization

It is generally believed that surfactant-free emulsion polymerization involves four steps: initiation, nucleation into primary particles, coagulation into secondary particles, and growth. By high resolution SEM-imaging of the intermediate polymerization products, the evolution of the morphology of the polymer particles has been followed. This allowed us, to our best knowledge for the first time, to visualize coagulative nucleation, which is the process where the primary nanoparticles aggregate into larger entities. The obtained visual information and data on particle size, number, and zeta potential, strongly suggest that coagulative termination is responsible for the coagulative nucleation phenomenon, resulting in a dispersion of fine, relatively uniform polymer particles.