The ISO 304 describes the measurement of the surface tension using a tensiometer and different sample bodies, such as a plate, stirrup or ring. It is used to characterise the effects of surface active agents on surface tension.
ISO 304: Application and Use
The surface tension is a fundamental property of every liquid and liquid mixture. The surface tension is defined as the force that acts along the surface of a liquid, trying to make the surface as small as possible. This force is usually measured in millinewtons per meter (mN/m). The standard ISO 304 specifies how to test the surface tension of solutions containing surface active agents. It can also be applied to pure liquids.
ISO 304: Experimentation
Apparatus
To conduct the method according to the ISO 304, 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 to hold the sample liquid
- a dynamometer (or balance), which can continuously measure the force applied to the measuring unit. The sample body is usually suspended from this balance
- a device for recording the measured values
The sample body is a small item, which is used to draw a liquid film from the sample liquid. According to the standard, different sample bodies can be used:
- rectangular plate
- a stirrup
- a ring
All Force Tensiometers of the DCAT series from DataPhysics Instruments comply with this standard.
Procedure
This standard describes the method for measuring the surface tension by drawing up liquid films. The sample body is suspended from the balance and dipped into the liquid, as specified in the standard. The sample body can be a rectangular plate, a stirrup, or a ring. As the surface tension varies over time, multiple measurements are recommended. The measurements of the surface tension should be recorded as a function of time. Some devices, such as the tensiometers of the DCAT series, can calculate the surface tension automatically.
The ISO 304 is in use since 1978, was last updated in 1985, added to in 1988, and last reviewed in 2019.
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