Abstract
The solubilization of hydrocarbons in aqueous solutions of surfactant-cosurfactant mixtures has been studied to determine the influence of counter ions on the solubilization and the effects of changing the oxyethylene chain length in both the ionic surfactants and in the cosurfactants. A microemulsion of cyclohexane was produced using a mixture of calcium or magnesium dodecyl poly (oxyethylene) sulfate and octyl poly (oxyethylene) ether. The solubilization power of this mixture was about six to eight times greater than that which contains univalent ionic surfactant. The presence of 2wt% sodium chloride in the aqueous solution of sodium dodecylmonooxyethylene sulfate and octyl di (oxyethylene) ether increased the solubilization power to more than six times that without sodium chloride. In systems without cosurfactant, addition of the oxyethylene chain into the ionic surfactants caused on increase of their solubilization power. However, it was shown that lengthening the oxyethylenechain of the ionic surfactants might decrease the solubilization power of surfactant-cosurfactant mixtures and change the optimal mixing ratio. On the other hand, the addition of the oxyethylene chain into the cosurfactants turned them from lipophilic to hydrophilic like nonionic surfactants; e.g., octyl tetra (oxyethylene) ether dissolved in water at 25°C. Consequently, the optimal mixing ratio of the solubilizers for the solubili-zation varied with the oxyethylene chain length of the cosurfactants. The concentration of surfactant-cosurfactant mixtures in the aqueous solutions also affected the solubilization power. Experimentally it was observed that an increase in the concentration of sodium dodecyl sulfate-octyl poly (oxyethylene) ether systems by a factor of two (from 5 to 10wt%) increased the solubilization power 1.6 times. The properties of the hydrocarbon also had an effect on the optimal mixing ratio and the solubilization power. The surfactant-cosurfactant mixtures seemed to be particularly useful in solubilizing long chain hydrocarbons. For example, dodecane was solubilized by a calcium dodecylmono (oxyethylene) sulfate-octyl di (oxyethylene) ether system about twenty fold greater than in the system without cosurfactant.
