Structured, Composite Nanoparticles from Emulsion Polymerization - Morphological Possibilities

Emulsion polymerization allows the creation of aqueous dispersions of polymer nanoparticles in the 50-500 nm size range, and these products (synthetic latexes) have been made at commercial scales for nearly a century. In the latter half of that period, there emerged a wide variety of nanoparticles composed of two, phase-incompatible materials producing composite particles having a large number of morphological features. Among those are the so-called core-shell, occluded, multilobed, hollow, and mixed structures. This has led to advanced materials serving markets for impact-resistant plastics, architectural and industrial coatings, adhesives, low density opacifiers, printing inks, among others. As the need for such materials has grown, the chemical and physical mechanisms that control the development of particle structure have been substantially investigated and much progress has been made. The objective of the following discussion is to describe the scientific and engineering principles at play when creating these composite particles and to demonstrate how the balance of thermodynamic equilibrium conditions and kinetic limitations (chemical reaction and polymer chain diffusion) combine and/or compete to result in particular morphologies. Many examples are presented.