Nucleation and Growth Process of Polystyrene Particle Investigated by AFM

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The nucleation and growth process of the polystyrene particles prepared by soap-free emulsion polymerization at the reaction temperature of 70°C are observed by dynamic light scattering (DLS), scanning electron microscopy (SEM) and atomic force microscopy (AFM). Here, the use of a cationic initiator enables us to synthesize the positively charged polystyrene, which then adsorbs electrostatically on the negatively charged mica plate with molecular scale smoothness. As a result, the followings are found.<BR>1. In the nucleation process, the monomers are polymerized by initiators and form polymers, and the polymers are coagulated and probably make micelle-like embryos, and then nuclei are generated. The nuclei absorb monomers in the bulk to form particles, such that the surfaces of the formed particles increase hydrophobicity. The hydrophobic particles are coagulated by their hydrophobic attractions. Through these processes, mono-dispersed particles are formed.<BR>2. In the growth of the mono-dispersed particles, they absorb the monomers in the bulk and swelling, and then become extremely soft. As the reaction time increases, the rigidity of the particles changes from soft to hard by their polymerization. In the present experimental system, polymeric materials are not born in the bulk continuously because of a small amount of initiators. That is why the growth by their deposition to the particle surface, so called hetero coagulation, can not be expected.

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