ABSTRACT
Previously we reported on the use of lipophilic, hydrophilic, and combined linkers for formulating microemulsions of trichloroethylene and tetrachloroethylene. These linker molecules augment the interaction between the surfactant and oil phase (lipophilic linkers) or between the surfactant and water phase (hydrophilic linkers). Combining both linkers can increase the solubilization capacity several-fold. This formulation technique shows potential advantage in reducing surfactant costs and remedial times, as well as allowing the use of more environmentally friendly additives when designing surfactant-enhanced remediation systems. In this paper, we evaluate the relative importance of the surfactant and each linker in increasing the system's solubilization capacity. This interpretation is based on solubilization curves, partitioning studies, and formulation studies. The solubilization curves show that optimum linker performance is reached at an equimolar ratio of dodecanol, used as a lipophilic linker, and sodium mono and dimethyl naphthalene sulfonate, used as a hydrophilic linker. Furthermore, this equimolar combination was able to replace the anionic surfactant sodium dihexylsulfosuccinate. Dodecanol partitioning at optimum formulation shows that the poor performance of lipophilic linkers alone is due to their low partitioning into the middle phase. Adding hydrophilic linkers into this system increases the fraction of dodecanol in the middle phase, thereby further enhancing the solubilization capacity of the system. A variation of the combined linker approach is introduced by changing a lipophilic linker, oleic acid, into a surfactant (soap), with further increases in the solubilization capacity by 4- to 5-fold.
