The OECD Test No. 115: Surface Tension of Aqueous Solutions outlines how to measure the surface tension of liquids using a force measurement conducted with a tensiometer. Three different methods are mentioned in the guideline: measuring with a ring, plate, and stirrup.
OECD Test No. 115: Application and Use
This guideline describes three methods to measure the surface tension of aqueous solutions. The tests are based on the measurement of force. To do so, a ring, plate or stirrup is suspended from a balance and brought into contact with the surface of the liquid. The detailed description of the three methods can be found in standard ISO 304.
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. Generally, the higher the surface tension, the higher the interactions within the phase. This means that liquids with higher surface tension are less likely to mix with another liquid phase.
OECD Test No. 115: Experimentation
Apparatus
To conduct tests according to this guideline, a tensiometer is needed. It consists of the following:
- moveable sample table
- force measuring system (balance)
- measuring body (ring, stirrup or plate)
- measurement vessel
All tensiometers of the DCAT series from DataPhysics Instruments comply to this guideline.
Procedure
Clean the vessel and the measuring body thoroughly. Before immersing the measuring body in the liquid, the balance should be adjusted to zero. The temperature of the sample liquid must be controlled. Then, the measuring body is submerged in the sample liquid and the force measured. From this value, the surface tension can be calculated.
The OECD Test No. 115 is in use since 1995. It is related to the standard ISO 304.
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