Investigations into the Mechanism of Formation of Water-in-Xylene Microemulsions Using Interfacial Tension Measurements

Abstract

Interfacial tension measurements using both the Wilhelmy plate and spinning drop methods showed that the addition of n-hexanol to the oil phase resulted in a reduction of the oil/water interfacial tension, γo/w, depending on the concentration of sodium dodecylbenzene sulphonate (NaDBS) in the aqueous phase. Moreover, some fluctuation in γo/w‚ was observed when the n-hexanol concentration was kept constant in the oil phase (10% w/v) and the NaDBS was increased above 10^-1 mol dm^-3; the interface became unstable leading to the formation of a viscous gel phase (liquid crystalline) and ultimately droplets began to form in the spinning drop apparatus. Injection experiments showed that, under conditions where a microemulsion is formed, a transient “negative” interfacial tension may be needed. This may be the result of redistribution of surfactant molecules and the formation of a “fluid-like” boundary with some liquid crystalline phase formation.