Measurement of interfacial tension between oil and an aqueous solution via a floating drop method

We describe a new measurement method for liquid–liquid interfacial tension via a floating droplet profile (floating drop method), on a liquid. The accuracy of the floating drop method was confirmed for an oil-aqueous solution system. Specifically, we measured the interfacial tension between a floating rapeseed oil droplet and a 0.2% aqueous solution of polyoxyethylene alkyl ether sulfuric acid ester salt. In addition, it was confirmed that the tensile balance at the edge of the oil droplet floating on the aqueous solution, which is known as Neumann’s triangle, is satisfied in the present system.