Equilibrium and dynamic behavior for systems containing nonionic surfactants, n-hexadecane, triolein and oleyl alcohol

Abstract

Phase behavior and electrical conductivity experiments were carried out for systems containing water, nonionic surfactants, triolein, n-hexadecane and oleyl alcohol. In systems where the amount of triolein was equal to or greater than the amount of n-hexadecane, the surfactant appeared successively in the lamellar liquid crystalline phase L α, the sponge phase D′, a bicontinuous microemulsion D and an oil-rich microemulsion O m as the system was made more lipophilic. The temperatures of the various phase transitions decreased with increasing hydrocarbon content. In one system five phases were found to coexist simultaneously: L α, D′, D, and excess water and oil. Conductivity measurements indicated no major change in microstructure of either D′ or D phases when the n-hexadecane-to-triolein ratio was changed from zero to one. In systems where the amount of hydrocarbon was much greater than the amount of triolein, the usual microemulsion phase behavior was seen with continuous variation of oil and water solubilization over a wide range. Videomicroscopy contacting experiments were consistent with the phase behavior results in that the D′ phase was observed as one intermediate phase when drops rich in triolein were injected into aqueous surfactant solutions but not when the drops were mainly hydrocarbon. In the latter case, microemulsions were seen which inverted continuously until the surfactant concentration in the drops became high enough that the lamellar phase formed.