Influence of phase orientation on dynamic interfacial tension measured by drop volume tensiometry

In processes involving two liquid phases, such as enhanced oil recovery, one phase is often present in a drop form (drop phase) while the other is in continuous form (bulk phase). In the present paper, the effect of such phase orientation on dynamic interfacial tension between the two phases formed by the partially miscible system composed of butanol-l and water has been investigated by using the method of drop volume tensiometry. With butanol-rich (butanol-l saturated by water) as the drop phase and water-rich (water saturated by butanol-l) as the bulk phase, the interfacial tension is 1.70 +/- 0.02 mN/m. The interfacial tension for water-rich as the drop phase is almost identical at 1.72 +/- 0.03 mN/m. Addition of a surfactant, sodium dodecyl sulfate, to the system has been studied. When the surfactant is added to the drop phase (either butanol-rich or water-rich), the magnitude of the decrease in interfacial tension is smaller than when surfactant is added to the bulk phase (water-rich or butanol-rich) or to bath phases. Under otherwise identical conditions, when the water-rich acts as the drop phase, the apparent interfacial tension is higher than that when the butanol-rich acts as the drop phase.