Molar solubilization ratio, determination

The amount of water solubilized in a reverse micelle solution is commonly referred to as W, the molar ratio of water to surfactant, and this is also a good qualitative indicator of micelle size. This is an extremely important parameter since it will determine the number of surfactant molecules per micelle and is the main factor affecting micelle size. For an (AOT)/iso-octane/H20 system, the maximum Wq is around 60 [16], and above this value the transparent reverse micelle solution becomes a turbid emulsion, and phase separation may occur. The effect of salt type and concentration on water solubilization is important. Cations with a smaller hydration size, but the same ionic charge, result in less solubilization than cations with a large hydration size [17,18]. Micelle size depends on the salt type and concentration, solvent, surfactant type and concentration, and also temperature. 

The next step was to measure the ability of the reverse micelles to solubilize water. Known amounts of water were injected into one-phase AOT-fluid systems, and the location of the pressure boundary between the one-phase and two-phase regions was determined. It is customary in AOT studies to express the amount of solubilized water in terms of Wq, the molar water/surfactant ratio [19]. In liquid systems the Wq value at which the system phase separates is known as This number can be as high as 100 for AOT in solvents such as pentane [12]. In ethane and propane, however, is much smaller and varies with pressure, as shown in Fig. 2 [10,20]. 

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