The ASTM D 1331 outlines test methods for measuring the surface and interfacial tension of solutions of paints, solvents, solutions of surface-active agents and other liquids. In detail, four measurement methods are described, using either the Du Noüy ring or the Wilhelmy plate method with a force tensiometer.
ASTM D 1331: Application and Use
The determination of the surface an interfacial tension of liquids gives and indication of their wetting properties. Often, surface active agents are used to lower the surface tension of a liquid. The ASTM D 1331 covers four measurements for many liquid materials, such as paints, solvents, and solutions of surface-active agents.
ASTM D 1331: Experimentation
Apparatus
For this measurement, the following apparatus is used:
- tensiometer
- Du Noüy ring (4-6 cm circumference platinum ring) or Wilhelmy plate out of glass or platinum
- sample container, with 6 cm minimum diameter
All Force Tensiometers of the DCAT series from DataPhysics Instruments comply with this standard.
Procedure
This standard includes four different measurements in total:
- Surface tension measurement using a Du Noüy ring
- Interfacial tension measurement using a Du Noüy ring
- Surface tension measurement using a Wilhelmy plate
- Interfacial tension measurement using a Wilhelmy plate
The standard advises to conduct the test at least twice, and more often if necessary. The temperature of the liquid as well as the time elapsed between submersion and the breakaway of the liquid from the ring or plate should be recorded.
With complete wettability, the contact angle is 0°. This means that the liquid spreads completely across the solid surface. With partial wettability, the contact angle is greater than 0° but less than 90°. In this case, the liquid does not fully wet the surface, instead forming a hemispherical drop. With poor wettability, the contact angle exceeds 90°. This means the liquid avoids the surface, and in extreme cases remains as a round drop.
The ASTM D 1331 is in use since 1989, was last updated in 2020 and last reviewed in 2024.
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