Experimental Methods of Studying Solubilisation

The concentration of solubilisate that can be incorporated into a given system with the maintenance of a single isotropic solution (saturation concentration or maximum additive concentration, MAC) is obtained using the same procedures for measurement of solubility of any compound in a given solvent [30]. Since solubilisation is temperature sensitive, adequate temperature control is essential. 

With solubilisates having significant water solubility, it is of interest to know both the distribution ratio of solubilisate between micelles and water under saturation and unsaturation conditions. To measure the distribution ratio under unsaturation conditions, a dialysis technique can be employed, using membranes that are permeable to solubilisate but not to micelles. Ultrafiltration and gel filtration techniques can be applied to obtain the above information. The data are treated using the phase-separation model of micellisation (micelles are considered to be a separate phase in equilibrium with monomers). 

The partition coefficient. Pm, between micelles and solution is given by 

Equation (13.25) does not include the volumes of the micellar or aqueous phase, which can be obtained from the partial molar values of the surfactant. A better expression is 

An alterative expression that treats solubilisation as a process of binding of solute molecules to binding sites on the surfactant is 

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