There are four different methods: the plate method, the stirrup method, the ring method and the OECD harmonized ring method.

Ring method according to Du Noüy: The force acting on an optimally wettable ring as a result of the tension of the withdrawn liquid lamella when removing the ring is measured in this method.

Because of the movement of the ring during the measurement, the ring method is only a quasi-static method which may not give the surface tension value at equilibrium for some samples.

The measuring probe is usually a ring (Du Noüy ring method) or a plate (Wilhelmy plate method).

D971 Test Method for Interfacial Tension of Oil Against Water by the Ring Method

Unlike the quasi-static Du Noüy ring method, in which the surface is deformed during the measurement, the plate method is purely static.

Unlike the quasi-static ring method according to du Noüy, in which the surface is deformed during the measurement, the plate method is purely static.

The wetted length is used in the calculation of the surface tension or interfacial tension in the Du Noüy ring method, the Wilhelmy plate method and in the rod method.

This device is used to measure the surface tension coefficient using the ring method (also known as the du Nouÿ ring method) for fluids with small and average surfactant concentrations (water, hot water, oil, alcohol, etc.).

This device is used to measure the surface tension coefficient using the ring method (also known as the du Nouÿ ring method) for fluids with small and average surfactant concentrations (water, hot water, oil, alcohol, etc.).