Particle nucleation Subject

The next event could be solidification of the oil into an amorphous solid or direct nucleation to a crystalline form. In either case, the fine particles are subject to agglomeration as the particles collide and stick together because of the oily/sticky nature of the solid surfaces at this point. Assuming a crystalline form results from this series of events, these nuclei can then grow to some extent, as determined by the system-specific characteristics of the compound. This process continues throughout the addition of the reagent(s). 

The most important characteristic of miniemulsion polymerization is the transformation of the homogenized monomer droplets into latex particles via the capture of free radicals when a water-soluble initiator such as the persulfate initiator is used to initiate the free radical polymer reactions. However, this feature does not necessarily guarantee that the particle nucleation mechanisms other than monomer droplet nucleation can be ruled out. As will be shown later, previous studies dealing with nucleation of particle nuclei in miniemulsion polymerization often resulted in controversial conclusions. This subject is still open to discussion, and it represents a great challenge to polymer scientists. 

Borkent BM, Arora M, Ohl CD, Jong ND, Versluis M, Lohse D, Morch KA, Klaseboer E, Khoo BC (2008) The acceleration of solid particles subjected to cavitation nucleation. J Fluid Mech 610 157-182... 

In view of secondary nucleation in crystallizers, Ten Cate et al. (2004) were interested in finding out locally about the frequencies of particle collisions in a suspension under the action of the turbulence of the liquid. To this end, they performed a DNS of a particle suspension in a periodic box subject to forced turbulent-flow conditions. In their DNS, the flow field around and between the interacting and colliding particles is fully resolved, while the particles are allowed to rotate in response to the surrounding turbulent-flow field. 

Of course (as always in a delicate subject like the present one) I have my own critiques on certain points in the presentation for instance, in Section 5.3.1, coalescence is attributed to the thermal nucleation of a pore between two adjacent droplets. For me, discussing this channel is like discussing the sex of angels. Nucleation, in most physical systems, does not occur via plain thermal fluctuations. It involves external defects a cosmic ray in a bubble chamber, or a dust particle in a condenser. I believe that the same holds for emulsions dust particles (or small surfactant aggregates) control coalescence. 

Because the subject is vast, the presentation is limited to a discussion of the uptake of a tracer from the vapor phase by spherical particles. This is the viewpoint of one concerned with fallout formation. The reverse process—escape from spherical particles—is the viewpoint of one concerned with reactor fuels. For the idealized case the treatment is exactly the same for the two situations. The fact that we deal with trace quantities and concentration means that we can neglect changes in the particle properties as the reaction proceeds and that we need not be concerned with surface nucleation. 

---