The emulsifier‐free emulsion polymerizations of styrene in the presence of the surface active comonomer, undecylenic isethionate sodium salt (at concentration below its critical micelle concentration), and of the initiator, potassium persulfate, indicate that the number of polymer particles and the rate of polymerization at steady state is dependent on 1‐power of the comonomer concentration and 1/2‐power of the initiator concentration. This result suggests a homogeneous nucleation mechanism by which particles are formed from coiled‐up oligomeric radical chains originally dissolved in the aqueous phase. Size distribution of the particles is rather narrow and has a uniformity very close to one (ca. 1.02) after 30% conversion. Addition of salt such as sodium sulfate to increase the ionic strength in the aqueous phase results in a formation of micelles (which can grow to become polymer particles) in addition to the formation of polymer particles through the homogeneous nucleation mechanism. Variation of the ionic strength leads to a variation in the number of polymer particles due to a competition between these two nucleation mechanisms and gives a minimum of the number of polymer particles and a maximum of the average particle diameter.

Lead zirconate titanate (Pb(1.1)(Zr(0.52)Ti(0.48))O(3)) thin films of thickness 260 nm on Pt/Ti/SiO(2)/Si substrates were densified by 2.45 GHz microwave annealing. The PZT thin films were annealed at various annealing temperatures from 400 to 700 °C for 30 min. X-ray diffraction showed that the pyrochlore phase was transformed to the perovskite phase at 450 °C and the film was fully crystallized. The secondary (again pyrochlore) phase was observed in the PZT thin films, which were annealed above 550 °C. The surface morphologies were changed above 550 °C of the PZT thin films due to the secondary phase. Higher dielectric constant (ε(r)) and lower dielectric loss coercive field (E(c)) were achieved for the 450 °C film than for the other annealed films.

SynopsisThe emulsifier-free emulsion polymerizations of styrene in the presence of about 0.33-2.7% (relative to styrene) of the water soluble comonomer, 2-hydroxyethyl methacrylate ( HEMA), and of the initiator, potassium persulfate ( K P S ) , were carried out. It was found that KPS plays a predominant role in the particle nucleation process, since the number density of polymer particles (N,) was dependent on the 0.97-power of [ KPS] . The nucleation ability of HEMA was weak, since N p was dependent only on the 0.17-power of [ HEMA]. The particle nucleation stage ceased quite early before 1% conversion, leading to nearly monodispersed polymer particles. The nucleation is suggested to be via the homogeneous nucleation mechanism. The particles grow via the core-shell structure mechanism (shell region polymerization), since the particle size is rather large-from 1500 to 6000 A. The amount of HEMA can affect the shell thickness and physical properties of the shell, such as the monomer swelling capacity and monomer diffusion rate.

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