Water pool size

Figure 12.15. Fluorescence lifetime of IR-140 in Aerosol OT (AOT)/iso-octane microemulsions as a function of water pool size to, defined as the molar fraction of water to AOT. (From Ref. 58.)...

In addition to the spectroscopic changes observed for cations 1 and 2 in the AOT reversed micelle, significant differences in the distribution of photoproducts are observed relative to that in homogeneous solution (Tables 2 and 3). At large co values, the photoproduct distribution is similar to concentrated aqueous acid solution with the cis isomer and the a dimer as the principle photoproducts. However as a> is decreased, the p dimer becomes the predominant photoproduct and the ratio of p/a reaches a maximum value at 10 for 4-stilbazolium and at -15-20 for 2-stilbazolium. Formation of the 8 dimer from cation 1 follows the same trend as the p dimer the amount of 8 dimer formed increases as the water pool size is reduced. Decreasing the ratio of [HStz]/[AOTl appears to have an effect similar to increasing on the photoproduct distribution. These results clearly demonstrate that the size of the water pool and/or... 

At low to values in the AOT reversed micelle, significantly more cis isomer is formed from cation 2 than from cation 1. This difference could be attributed to a difference in the alignment at the interface, reactivity, or pKa values between the two cations. The absorption spectrum of 2-stilbazole is significantly blue shifted relative to the protonated form. The slight blue shift of the 2-stilbazolium absorption spectrum with increasing co could suggest that deprotonation occurs with increasing water pool size. 

Increasing the water pool size reduces the curvature at the interface and could decrease the overlap between monomers needed for bimolecular reactions to occur. 

During the study period, the Hz O method assumes no changes in body water pool sizes. This assumption might be appropriate for adults of stable weight, but would not be appropriate for premature infants. 

CONTROL OF THE WATER POOL SIZE IN REVERSE MICROEMULSIONS... 

What are the factors that might control the water pool size It has been found by many workers that the most important controlling factor is the molar ratio w = [water] /[surfactant] and the nature of the continuous phase may not play a very significant role. Kotlarchyk etal. [148] studied the system NaA0T/n-decane/D20 by small-angle neutron scattering and proposed a relationship ... 

There are, of course, cases where the concept of correspondence between pool size and particle size seems to have been realized. One example is the synthesis of cadmium sulfide particles in W/CO2 microemulsions [229]. This work shows that the average nanocrystal radius was comparable with the corresponding water pool size. 

As expected, the particle size (2/ p) increased with the w value and the water pool size 2/ , as discussed earlier (Table 5.2). 

With high values of w, polydispersity became prominent. Further, the particle size was found to be slightly larger than the water pool size. Finally, both size and polydispersity of the particles increased with the concentration of copper in the water pool. 

Nagy [242] has discussed in detail the parameters to be optimized and the conditions to be established in W/O microemulsions for synthesis of metals and metal borides. Parameters that demand attention for standardization of a microemulsion system are the (a) water pool size (dependent on the w value), (b) changes brought about by dissolved reactants, (c) a possible percolation phenomenon in the system, (d) site of solvation of the precursor ions, (e) distribution of the reactants in the droplets and (f) exchange rate among the reactants. 

TABLE 1 Conductometricaily Estimated Water Pool Size Overall Droplet Dimension (R ), Surfactant Aggregation Number (A,), and Cosurfactant Aggregation Number (A,)per Droplet tor a Number of W O Microemulsions at 293 K at Constant Weight Fraction of Water = 0.2 and Surfactant Cosurfactant Weight Ratio = 0.5... 

---