|Molecular-Scale Investigation of Nucleation and Growth Process
of Polystyrene Latex Particles
Department of Chemical Engineering, Kyoto University-Katsura, Kyoto, Japan
Nippon Gomu Kyokaishi,(2006),79(2),54-60 General Review in Japanese
To clarify the mechanism of nucleation and growth process in the soap-free polymerization of styrene in water, the polymerization process of styrene was investigated on the molecular scale, using an atomic force microscope (AFM), as well as a scanning electron microscope (SEM) and a dynamic light scattering apparatus (DLS). A cationic initiator was employed to make polymerized styrene adsorb electrostatically on the negatively-charged mica plate with molecular-scale smooth surface and the mechanism was estimated from AFM measurements in-situ in water.
The followings were found. (1) Monomers in the bulk are polymerized by initiators and form nuclei coagulated by the hydrophobic attraction between their alkyl chains. (2) As far as the initiators and monomers remain in the bulk solution, the polymeric materials (oligomers, embryo, nucleus, and solidified nucleus) are born in the bulk continuously. (3) The growth is due to the deposition of polymeric materials in the bulk on the particle surface and their simultaneous swelling by monomers in the bulk.
(4) The reason why the particle size increases with increasing concentration of initiator is that the main growth of particles is due to the deposition of polymeric materials in the bulk whose amount increases with the initiator concentration.
Nucleation, Growth, Soap-free polymerization, AFM