Enhanced aqueous solubility of naphthalene and pyrene by binary and ternary Gemini cationic and conventional nonionic surfactants

A systematic study has been carried out to get insight into the micellar behavior of Gemini cationic and conventional nonionic in their single as well as equimolar bi and ternary mixed state using the technique of tensiometry. The models proposed by Clint, Rubingh and Motomura et al. have been employed to interpret the formation of mixed micelles and find out synergism. The obtained experimental CMCs are lower than the ideal CMCs, indicating negative deviation from ideal behavior for all multi-component mixed micelles formation. The solubilization capacities of selected equimolar bi and ternary surfactant systems towards polycyclic aromatic hydrocarbons (PAHs), naphthalene and pyrene, have been evaluated from measurements of the molar solubilization ratio (MSR), the micelle-water partition coefficient (K(m)), the deviation ratio (R) and the free energy of solubilization (ΔG(s)(0)) of PAHs. The results show that the solubility of naphthalene and pyrene over that in water in case of Gemini cationic surfactant is dramatically enhanced by adding equimolar nonionic surfactant in both bi and ternary mixed surfactant systems. The studied equimolar ternary surfactant system shows higher solubilizing efficiency than Gemini cationic binary system but lower than their cationic-nonionic counterpart. In addition, the solubilizing power of multi-component mixed surfactants towards naphthalene and pyrene increases with increasing logK(ow) of PAHs. Certainly, the solubilization abilities of the selected surfactants not only depend on their structure and mixing effect but also associate with solubilizing microenvironment and chemical nature of organic solutes.