System behavior, size influence

A change in size on scale-up is not the sole determinant of the seal-ability of a unit operation or process. Scalability depends on the unit operation mechanism(s) or system properties involved. Some mechanisms or system properties relevant to dispersions are listed in Table 2 (59). In a number of instances, size has little or no influence on processing or on system behavior. Thus, scale-up will not affect chemical kinetics or thermodynamics although the thermal effects of a reaction could perturb a system, e.g., by affecting convection (59). Heat or mass transfer within or between phases is indirectly affected by changes in size while convection is directly... 

Table 2 Influence of Size on System Behavior or Important Unit Operation Mechanisms...

System behavior or unit operation mechanisms Important variables Influence of size... 

Cholesteryl myristate nanoparticles are excellent model systems to study the phase behavior and influencing parameters like particle size and stabilizer system, but are not applicable as robust drug carrier system due to their relatively high crystallization temperature (above or around 0°C). As storage at 4°C appears advantageous with respect to the chemical stability of the dispersions a robust formulation should allow long-term storage at this temperature without nanoparticle crystallization. 

Our system provides for several forms of calibration function, but we generally use "universal" calibration (5) and represent the dependence of the logarithm of hydrodynamic volume on retention volume by a polynomial, as in Figure 6. Note that the slope of the function changes dramatically near the ends of the range of applicability. The calibrants at the ends of the range exert a dramatic influence on the form of the fitted polynomial. This behavior demonstrates that the column set must be carefully chosen to fractionate the desired range of molecular sizes. 

The shade of a product is another parameter which is influenced by the particle size (Sec. 1.6.1.2). This is easy to see by comparing the reflection curves of two Pigment Yellow 83 white reductions in an alkyd-melamine resin system. The electron photomicrographs in Fig. 65 and the particle size distribution histograms in Fig. 66 represent these samples. At equal pigment concentration, curve 1 of the two remission curves in Fig. 67 reflects the behavior of the pigment with the smaller... 

Supported bimetallic catalysts have gained unquestionable importance in subjects such as refining, petrochemistry and fine chemistry since their earliest use in the 1950s [1, 2]. The catalytic behavior of such a system is influenced by the size of the metal particles and by the interactions among them and with the support and other catalyst components. The second metal may influence the first metal through electronic interactions or by modifying the architecture of the active site. Very often, the interactions between the two metals are complex and largely unknown, and consequently the preparation procedure critically influences the nature of the catalytic system obtained. 

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