Investigation on the solubilization of polycyclic aromatic hydrocarbons in the presence of single and mixed Gemini surfactants

Water solubility enhancements of naphthalene (Naph), phenanthrene (Phen) and pyrene (Py) by a series of single cationic Gemini surfactants (CG(s), s=4, 8, 12 and 16) as well as their equimolar binary combinations (CG(12-m), m=4, 8 and 16) have been investigated. The relationships between their surface properties and solubilizing capacities toward three polycyclic aromatic hydrocarbons (PAHs) have been quantified and discussed. The selected single Gemini surfactants observably enhance the water solubility of PAHs following the order of Phen>Py>Naph except for CG(8) which has a superior solubilizing ability for Py. For the same organic compound, the solubilizing abilities of single Gemini surfactants are in tune with the order of variation tendencies of CMC values. However, the different mixed Gemini surfactant systems have shown selective solubilization on various PAHs which is not simply related to their mixed molar properties. Particularly, the CG(12-16) surfactant has relatively comparable solubilization on Py and inferior solubilization on Phen compared to all other investigated solubilizing systems. It is presumably attributed to the relationships between the structure of surfactants and the chemical nature of both solutes and surfactants. The analysis studied herein has provided valuable information for the selection of mixed Gemini surfactants for solubilizing water-insoluble compounds.