Solubilization of naphthalene and pyrene by sodium dodecyl sulfate (SDS) and polyoxyethylenesorbitan monooleate (Tween 80) mixed micelles

Water solubility enhancement of naphthalene and pyrene by micellar solutions of single (SDS, Tween 80) and mixed SDS-Tween 80 surfactants were investigated and compared. Molar solubilization ratios (MSRs) of naphthalene (0.065 in SDS and 0.301 in Tween 80) and pyrene (0.010 in SDS and 0.083 in Tween 80) agree relatively well with the reported literature values. In SDS-Tween mixed micelles, MSRs of naphthalene were found to increase with increasing Tween 80 mole fraction. This was related in part to the decrease in the CMC of the mixed SDS-Tween 80 surfactant systems. Naphthalene experimental molar solubilization ratios (MSRexp) in mixed micelles were found to be similar to those derived from ideal mixing rule (MSRid), indicating no SDS-Tween 80 mixing effect on naphthalene solubilization. On the other hand, MSRexp of pyrene in SDS-Tween 80 mixed micelles were larger than the MSRid at all SDS-Tween 80 surfactant composition ranges, suggesting a positive deviation (synergism) from ideal mixing rule. The origin of synergism for solubilization was explained in terms of surfactant–surfactant interaction occurring within the solubilization site of the organic solute.