Water solubilization capacity

In some systems containing surfactant mixtures, a synergistic effect on the water solubilization capacity has been observed [50]. 

This Is approximately 25 times reduction of water solubilizing capacity with only 5% polymer of a modest molecular weight. This result Is a good Illustration of the Incompatablllty of polymers and mlcroemulslons and the Initial lack of success (13) In polymerization Is a reasonable result. 

Figure 7. Effect of Alcohol and Oil Chain Length on Water Solubilization Capacity of Sodium Stearate Containing Microemulsions.

The susceptibility of microemulsions to destabilization by electrolytes severely limits the highest metal concentrations that can be used for precipitation reactions. This, in turn, discourages the large-scale application of microemulsion-mediated materials synthesis. A possible approach to tackling this problem appears to lie in the judicious selection of cosurfactants for microemulsion formulations. Darab et al. [125] reported that addition of SDS to the AOT/isooctane/water microemulsion increased dramatically the tolerable concentration of metal salts in the water pools. According to Chhabra et al. [50], addition of -hexanol to the Triton X-lOO/cyclohexane/water microemulsion led to a significant improvement in the water-solubilizing capacity. 

Rabie et al [ 122] reported similar results with heptanol, a relatively long-chain alcohol in the system AOT/decane/water and showed that by using the titration method (see Section 3.3), the value of w (around 45 in absence of heptanol) increased to about 90 with a heptanol/AOT molar ratio of about 0.35. As expected, the w value decreased drastically with further addition of heptanol. It was concluded that when in excess, the alcohol acts as a co-solvent rather than a co-surfactant. The observation of Caillet et al. [ 126] that the water solubilization capacity of different alcohols ([ 1 -alkanol]/[AOT] = 0.5, temperature 25"C) reaches a peak in the system AOT/n-decane/ water with increase of the chain length up to C7 has been already mentioned. As for benzene, not a usual co-surfactant, Rabie et al. [122] confirmed a rise of w from about 45 to a peak of 75 at a benzene/AOT molar ratio close to 10. 

The critical temperature of microemulsions, traditionally modified by adding salts, has been decreased by incorporation of [C mim][BFJ in water/AOT/decane microemulsions [110, 111]. This study showed that the amount of [C, mim][BFJ needed for curvature adjustment in ionic microemulsions was less than the amount of NaCl normally used. The water solubilization capacity in water/AOT/isooctane microemulsions in the presence of IL has been investigated for [Cjmim][Cl], [C mim] [Cl], and [Cgmim][Cl] showing an enhanced solubility at low IL concentrations but a... 

B.K. Paul and R.K. Mitra 2005 Water solubilization capacity of mixed reverse micelles Effect of surfactant component, the nature of the oil, and electrolyte concentration, J. Colloid Interf. Sci. 288, 261-279. 

Figure 5.4 Variations of the maximum water solubilization capacity per AOT molecule ( ) (left scale w = [H20]/[A0T]) and conductivity measured near the phase limit (+) (right scale) with the NaCl concentration. Initial AOT/decane = 25/75 (wt(wt). T = 25°C. See Section VI.C for the meaning of R = and R and Section VII.C for w i, W(jf, AW(j. Reprinted with permission from Reference 134, copyright 1998, American Chemical Society.

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