This standard specifies a test method, which uses the measurement of the volume of a drop, to determine the interfacial tension between two liquid phases. This standard is very suitable for the determination of the interfacial tension of aqueous or organic solutions of surfactants. It presents certain advantages over the method that studies the stretching of a liquid interfacial film (see standard UNE 55-708). These advantages are the following:
——Determination of interfacial tension for solutions containing any type of surfactant, including cationic surfactants. - Measurement, with sufficient precision, of low interfacial tensions, of the order of 1 mN/m. - Standard deviation of repeatability less than ±0.5 mN/m, which is an acceptable value for control in industrial laboratories. - Determination of the interfacial tension of viscous liquids. - Determination of interfacial tension using small amounts of solution. - Determination of the variation, over time, of interfacial tension, by means of an automatic device.