Influence of Phase Orientation on the Measurement of Interfacial Tension by Spinning Drop Tensiometry

The effect of phase orientation on the apparent interfacial tension measured by the spinning drop technique was investigated using the butanol-1/water two-phase system. Addition of a surfactant to the butanol-rich droplet produced a time-dependent IFT which slowly increased to a constant value of about 1.3 mN/m. When the surfactant was added to the water-rich external phase, the IFT was constant at 0.8 mN/m, which was identical with that when the surfactant was added to both phases.