A tensiometer is a device for measuring the surface tension of a liquid and/or the interfacial tension between two liquids.
There are different types of tensiometers with different measuring methods for particular measuring ranges and problems:
- Force tensiometer: The tensile force which occurs as a result of wetting an immersed probe is measured with reference to the wetted length. The measuring probe is usually a ring (Du Noüy ring method) or a plate (Wilhelmy plate method). For measuring static interfacial tension and surface tension in the medium to upper measuring range (1-100 mN/m).
- Bubble pressure tensiometer: The maximum internal pressure of a gas bubble which is formed in a liquid by means of a capillary is measured. For measuring dynamic surface tension as a function of surface age.
- Drop volume tensiometer: The volume of a drop of liquid produced at a vertical capillary in another liquid is measured at the moment of its detachment. More rarely, it is also used for measuring the surface tension (drop phase in air). For measuring the dynamic interfacial tension as a function of interface age.
- Spinning drop tensiometer: A horizontal capillary filled with a bulk phase and a drop phase is set in rotation. The diameter of the drop which is elongated by centrifugal force correlates with the interfacial tension. For measuring the static interfacial tension, particularly suitable for very small interfacial tensions.
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