Effect of Electrolytes on the Pyrene Solubilization Capacity of Dodecyl Sulfate Micelles

Abstract

Micellar aggregation numbers for ionic surfactants are sensitive to both the ionic strength and the type of counterion present. The current study considers the effects of electrolyte conditions on solubilization of pyrene, a polycyclic aromatic hydrocarbon, in micellar dodecyl sulfate surfactant solutions. We use ultraviolet−visible spectrophometry to measure the pyrene solubilizing powers, and we use an excimer fluorescence technique both to measure the micellar aggregation numbers in the presence of pyrene solubilizates and to measure the pyrene solubilization capacities. The aggregation number increases with increasing concentration of background electrolyte. When considering different types of counterions (NH4+, Na+, and Li+), the aggregation number increases with increasing counterion binding affinity. We estimate the latter by electrical conductivity measurements. In all cases of varying electrolyte conditions examined, the solubilization capacity increases siginficantly with increasing aggregation numbers, and the solubilizing power is therefore only weakly dependent on the electrolyte conditions.