Particles nucleation and

The debate as to which mechanism controls particle nucleation continues. There is strong evidence the HUFT and coagulation theories hold tme for the more water-soluble monomers. What remains at issue are the relative rates of micellar entry, homogeneous particle nucleation, and coagulative nucleation when surfactant is present at concentrations above its CMC. It is reasonable to assume each mechanism plays a role, depending on the nature and conditions of the polymerization (26). 

Eisele, F. L., and P. H. McMurry, Recent Progress in Understanding Particle Nucleation and Growth, Philos. Trans. R. Soc. London, 352, 191-201 (1997). 

Particle nucleation and sintering in supported metal catalysts... 

The emulsifier provides sites for the particle nucleation and stabilizes growing or the final polymer particles. Even though conventional emulsifiers (anionic, cationic, and nonionic) are commonly used in emulsion polymerization, other non-conventional ones are also used they include reactive emulsifiers and amphiphilic macromonomers. Reactive emulsifiers and macromonomers, which are surface active emulsifiers with an unsaturated group, are chemically bound to the surface of polymer particles. This strongly reduces the critical amount of emulsifier needed for stabilization of polymer particles, desorption of emulsifier from particles, formation of distinct emulsifier domains during film formation, and water sensitivity of the latex film. 

Figure 7. Particle nucleation and growth kinetics determined by laser light scattering Rayleigh ratio vs. time. Exp. 1 no surfactant present Exp. 2 (SDS) = 6 X 10 4 mol dm 3. Theor Calculated from Curve 4, Figure 5, considering particle growth by polymerization.

Films grown by chemical vapor deposition are similar to the films described above, with one exception. The CVD process allows for the possibility of gas phase particle nucleation, and the incorporation of such particles in a growing surface can contribute to a surface roughness. This is one reason that atmospheric CVD is being used less and less, as compared to low-pressure CVD where such gas phase nucleation is less likely. 

Fig. 6. Schematic model for the particle nucleation and growth of sterically stabilized particles in dispersion polymerization using macromonomer...

Asua and Schoonbrood [49] have produced an extensive review of the literature dealing with copolymerization of Surfmers, of the Surfmers polymerization loci and the influence of Surfmers on particle nucleation and growth. From this, they concluded that the main feature of a Surfmer is its intrinsic reactivity and provided suggestions for the choice of the reactive group in a Surfmer. They also made proposals to maximize Surfmer performance and effectiveness, namely ... 

Macro- and miniemulsion polymerization in a PFR/CSTR train was modeled by Samer and Schork [64]. Since particle nucleation and growth are coupled for macroemulsion polymerization in a CSTR, the number of particles formed in a CSTR only is a fraction of the number of particles generated in a batch reactor. For this reason, their results showed that a PFR upstream of a CSTR has a dramatic effect on the number of particles and the rate of polymerization in the CSTR. In fact, the CSTR was found to produce only 20% of the number of particles generated in a PFR/CSTR train with the same total residence time as the CSTR alone. By contrast, since miniemulsions are dominated by droplet nucleation, the use of a PFR prereactor had a negligible effect on the rate of polymerization in the CSTR. The number of particles generated in the CSTR was 100% of the number of particles generated in a PFR/CSTR train with the same total residence time as the CSTR alone. 

The most successful NQD preparations with respect to nanocrystal quality and monodispersity entail pyrolysis of metal-organic precursors in hot coordinating solvents (120 360 °C). Understood in terms of La Mer and Dinegar s studies of colloidal particle nucleation and growth, these preparative routes involve a temporally discrete nucleation event followed by relatively rapid growth from solution-phase monomers and finally slower growth by Ostwald... 

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