Measurement of liquid/liquid interfacial tension with water on liquid paraffin by the floating drop method

[Display omitted] •Interfacial tension between water and liquid paraffin was measured by floating drop method.•A clear submerged profile of a heavier water droplet floating on a lighter liquid paraffin was observed.•Larger droplet was found to improve the accuracy of the measured value based on measurement and simulation.•Floating drop method with a heavier droplet on a lighter liquid is an effectual method for interfacial tension measurement. A floating drop method has the potential of high accurate interfacial tension measurement for liquid-liquid. In order to clarify its validity, the verification of the method should be carried out based on the liquid-liquid system where its interfacial tension is available. We measured the interfacial tension between water and liquid paraffin via a floating drop method by observing a clear submerged profile of heavier water droplet floating on lighter liquid paraffin. We then investigated the effect of the droplet size on the interfacial tension. Large droplets were found to improve the accuracy of the measured values, as demonstrated by a simulation based on the Laplace equation. The measured interfacial tension was 50.5 mN/m, which reasonably agrees with the values reported in the literature. We conclude that the floating drop method with a heavy droplet on a light liquid is effective for measuring the interfacial tension.