The ISO 6889 outlines the measurement of the interfacial tension between two immiscible liquids containing non-ionic or anionic surface active agents. The measurement is conducted with a force tensiometer using either the stirrup or ring method.
ISO 6889: Application and Use
The interfacial tension is a fundamental property of liquid mixture with at least two immiscible phases. The interfacial tension is defined as the force that acts along the surface of a liquid, trying to make the interface as small as possible. It is usually measured in Newtons per meter (N/m). The standard ISO 6889 specifies how to test the interfacial tension of liquid phases containing anionic or non-ionic surface active agents. It cannot be used for mixtures containing cationic surface active agents.
ISO 6889: Experimentation
Apparatus
To conduct the method according to the ISO 6889, a tensiometer is needed. In this standard, a tensiometer is defined as consisting of:
- a horizontal platform (on which the measuring cup will rest) which can be moved up and down
- a measuring cup
- a dynamometer (or balance), which can measure force continuously. The measuring unit is usually suspended from this balance
- a device for recording the measured values
According to the standard, different measuring units can be used:
All Force Tensiometers of the DCAT series from DataPhysics Instruments comply with this standard.
Procedure
This standard describes the method for measuring the interfacial tension by drawing up liquid films at the interface between two liquids that do not mix, using either a stirrup or ring. The measurement is conducted at the moment of maximum force, shortly before the film breaks off.
The ISO 6889 was last updated in 1986, and last reviewed in 2019.
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