Mixtures nucleation rate

The polymerization temperature, through its effects on the kinetics of polymerization, is a particularly effective means of control, allowing the preparation of macroporous polymers with different pore size distributions from a single composition of the polymerization mixture. The effect of the temperature can be readily explained in terms of the nucleation rates, and the shift in pore size distribution induced by changes in the polymerization temperature can be accounted for by the difference in the number of nuclei that result from these changes [61,62]. For example, while the sharp maximum of the pore size distribution profile for monoliths prepared at a temperature of 70 °C is close to 1000 nm, a very broad pore size distribution curve spanning from 10 to 1000 nm with no distinct maximum is typical for monolith prepared from the same mixture at 130°C [63]. 

However, the retarded nucleation rate towards ZSM-5 in the presence of DMSO or TEA, relative to TPA (see Figures 5 and 6) is quite unexpected on the basis of the composition of the starting mixture and this finding would seem to refute a precursor role for the D5R during nucleation. 

Jaecker-Voirol A, Mirabel P (1988) Nucleation rate in a binaiy mixture of sidfuric-acid and water- vapor. JPhys Chem 92 3518-3521... 

However, if we use the expressions for the classical nucleation rate, we also do not find the large increase in radius that is possible. Furthermore, Weres et al. (57) state that addition of NaCl to a homogeneous nucleating solution of silicic acid in water has only a moderate effect if the concentrations are below 1 M. Addition of salt to the reaction mixture of the Stober process has, however, very large effects. Clearly, classical nucleation cannot explain all the features of the Stober synthesis either. 

The presence of impurities can increase nucleation densities. Higher nucleation rates can be obtained with halogen/hydrogen mixtures than with methane/hydrogen mixtures. The presence of a large amount of oxygen in a plasma etches the sp carbon phase which nucleates more easily than diamond, and the Quality and yield of diamond particles may be improved... 

The process is called mixed suspension-mixedproduct removal crystallization. Because of the above restraints, the nucleation rate, in number of nuclei generated in unit time and unit volume of mother liquor, is constant at all points in the magma the rate of growth, in length per unit time, is constant and independent of crystal size and location all volume elements of mother liquor contain a mixture of particles ranging in size from nuclei to large crystals and the particle-size distribution is independent of location in the crystallizer and is identical to the size distribution in the product. 

Within this general framework there have been many different systems modelled and the dynamical, statistical prefactors have been calculated. These are detailed in [42]. For a binary mixture, phase separating from an initially metastable state, the work of Langer and Schwartz [48] using the Langer theory [47] gives the nucleation rate as... 

Jaecker-Voirol, A., and Mirabel, P. (1988) Nucleation rate in a binary mixture of sulfuric acid and water vapor, J. Phys. Chem. 92, 3518-3521. 

The induction time in homogeneous nucleation of a or p polymorphs of quizalofop-ethyl, i.e. the time the crystals first appeared in a supersaturated solution of quizalofop-e yl-ethanol mixtures was measured at temperatures between 293 and 31 IK in a batch stirred crystallizer. Experimental equations on the induction time have been derived semiquantitatively on the basis of an equation of classical nucleation rate. In addition, the concentration of supersaturated... 

However, the effect of temperature can be reversed if a very poor solvent is used, such as dodecanol for the polymerization of styrene and divinylbenzene. In such a case, the temperature affects the solvency, which in turn controls the phase separation of the polymers from solution. As the temperature increases, the solubility of the polymer in the porogen increases. The precipitation may occur when the nuclei reach a higher molecular weight. Therefore, the nuclei and the pores between them are larger. Frechet and Svec et al. found that this effect was not apparent, however, when mixtures of a very good solvent and a poor solvent were used. In these cases, the pore size is again controlled by nucleation rates [20]. 

Figure 1 Change of gas concentration in the reaction mixture during foaming and its effect on bubble nucleation rate. nucleation rate RSN, rapid self-nucleation with partial release of saturation GBD, growth by diffusion S, saturation CLS, critical limiting super saturation. 

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