Growing particles

During Stage II the growing particles maintain a nearly constant monomer concentration. The concentration of monomer is particle-size dependent, with smaller particles having lower concentrations (28). 

T. Pusztai, L. Granasy. Monte Carlo simulation of first-order phase transformations with mutual blocking of anisotropically growing particles up to all relevant orders. Phys Rev B 57 14110, 1998. 

We have already covered the first three in some detail. Impingement involves the point where the growing particles actually touch each other and have used up aU of the nutrient which had originally caused them to start growing. 

Boudart [4] TOFs can either be independent of particle size (structure-insensitive reactions), increase (antipathetic structure sensitivity) or decrease (sympathetic structure sensitivity) with growing particle size, or cross a maximum (Figure 2). 

In linear EP of bifunctional monomers, such as S, with water soluble initiators, the monomer droplets do not compete with micelles in capturing radicals from the aqueous phase because the total surface area of the droplets is much smaller than that of micelles and growing particles. Nevertheless, if some radicals enter monomer droplets, rapid termination takes place. Therefore, polymerization in monomer droplets is negligible [88]. However, if in the crosslinking EP of 1,4-DVB a few radicals are captured by monomer droplets, they can polymerize completely because the recombination of radicals is suppressed by the gel effect. Moreover, in thermal initiation or in initiation by hydrophobic initiators, such as AIBN, radicals are formed predominantly in the hydrophobic phase, i.e. in monomer droplets and in micelles, and crosslinking EP is initiated in the organic phase. 

Due to the reduced absorption of monomers and the low rate of polymerization in the micelles, the diffusion of monomer molecules from droplets to the growing particles is limited. Correspondingly, the probability of polymerization in the droplets increases. 

As the gel progressively dissolves to yield Si-richer zeolitic phases, the EDX and PIGE Si/Al ratios become closer. However, even for a 100 % crystalline phase, less A1 is still probed by EDX. This suggests that the A-synthesis ZSM-5 crystals must still contain some Al-rich amorphous phase, deeply embedded within the large particles, as to partially escape the EDX probing. For the same reason, the XPS also continuously probes the outer Si-rich layer of the growing particles. However, at the end of the crystallization, more A1 is detected on the outer rim than in the... 

In principle, silica growth kinetics may be controlled by (1) slow release of monomer via alkoxide hydrolysis in the particle-free reverse micelles, (2) slow surface reaction of monomer addition to the growing particle, and (3) slow transport processes as determined by the dynamics of intermicellar mass transfer. There is strong experimental evidence to support the view that the rate of silica growth in the microemulsion environment is controlled by the rate of hydrolysis of TEOS (23,24,29). Silica growth kinetics can be analyzed in terms of the overall hydrolysis and condensation reactions ... 

Fig. 3.2.6 Schematic diagram of equilibrium and steady levels of free Cd2+ concentration in the absence or presence of NH , showing the role of NH3 on the nucleation and growth of the monodisperse CdS particles, where the open and closed circles represent the solute ions and growing particles, respectively. (From Ref. 5.)...

During the subsequent growth step each nuclei gives rise to one nonporous final particle without any coalescence between the nuclei or the growing particles. 

Fig. 1.1 Energetics of nucleation. The critical radius, Rc, depends on the balance between surface and volume energies of the growing particle.

---