Reaction-controlled growth

In another communication using w/o microemulsions containing a nonionic surfactant, it is shown that TEOS hydrolysis and siUca-particle growth occur at the same rate, indicating the growth of siUca particles is rate-controlled by the hydrolysis of TEOS [54], The rate of TEOS hydrolysis also depends on the surfactant concentration, which controls the molecular contact between hydroxyl ions and TEOS in solution. Because of the reaction-controlled growth mechanism, the silica-particle size distribution remains virtually same over the growth period. 

Surface reaction controlled growth Diffusion-controlled growth... 

Therefore, the most efficient preparation of monodispersed particles can be achieved by regulating the feed rate of reactants (= — dC/dt) as proportional to tm in the case of diffusion-controlled growth and to t1 in the case of reaction-controlled growth, as illustrated in Fig. 4.1.10. 

Fig. 4.1.10 Maximum consumption rates of solute as a function of time for diffusion-controlled growth and reaction-controlled growth.

The main objective of this section is to theoretically compare aerosol size spectra evolving by the mechanisms of diffusion-, surface reaction-, and volume reaction-controlled growth. The results will provide a basis for the interpretation of atmospheric and laboratory aerosol size spectra with respect to the original growth mechanisms. 

The second case we consider is that of surface reaction-controlled growth, namely, when the rate of particle growth is controlled by the rate at which adsorbed A on the particle surface is converted to another species B. Thus we take, as the simplest representation of such a situation, the sequence. 

Figure 15.5. Variation of particle growth rate do/dt for interface reaction-controlled growth (Eq. (15.18)).

Consider two separate particles with a radius of r and ri, respectively, in a liquid. Draw schematically the solute distributions in the liquid between the particles for diffusion and reaction-controlled growth, respectively. For reaction-controlled growth, are there any differences between the solute distribution in the LSW theory and those in dissolution-controlled growth and precipitation-controlled growth Explain. 

---