Noble phase behavior of water/propanol/polyethyleneglycol mono alkyl ether/oil system

We studied the phase behavior of three coexisting phases in water/propanol/octaethyleneglycol mono dodecyl ether/heptane system at 45°C. A cone-like three-phase body was found in a composition tetrahedron. In the body aqueous and surfactant phases coexist in the presence of the third coexisting phase, an oil phase, with their loci of composition drawing a closed-loop on addition of propanol. The oil phase remains in an oil-rich region without major change in its composition. The roles of propanol are discussed by using hydrophile-lipophile balance and locations of critical tie lines. Propanol mainly plays two roles; one is as a lipophilic cosurfactant and the other is as a water-soluble cosolvent. The compositions of the critical end points were also determined by a method to use the critical tie line as a clue. In other systems the same pattern phase behavior was observed.