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FAQ - Process parameter surface tension

Are the measuring results comparable to the Du Noüy method?

A direct comparision is not possible. The Du Noüy method is a static method to measure surface tension, whereas the bubble pressure method due to the finite bubble lifetimes is a dynamic method of measuring.

The longer the bubble lifetime (= high surface age) the more the measured value of the dynamic method approaches the value of the static method. For this reason, it is also called measuring in the semi-static range. The time variation of the surface tension is mostly dependable on the surfactant being tested, its concentration and thus, a bubble lifetime of 60s or 100s is sufficient for measuring in the semi-static range.

Which influence does the viscosity of the liquid have?

With dynamic measurements measuring results are subject to the influence of the viscosity which is highest for short bubble lifetimes and at high viscosity. The viscosity does not have any influence on aqueous solutions. Liquids that are more viscous than water should possibly be measured at a higher bubble lifetime.

How should the sample be handled?

Generally, many samples can be measured in one vessel. Certain samples, i.e. demulsifying systems have to be adequatly mixed and temporated while measuring without disturbing the measurement. For that SITA offers adjusted tensiometer accessories.

Why having an automatic process control?

During the cleaning process surfactants are bound at the surface of parts and on contamination as well as removed by filtration. The point of time and to which extent a cleaning bath has to be maintained are based on the cleaning result or already existing empirical values. A continuous analysis of the process condition is essential in order to ensure an optimal dosage of surfactants and an economical process management.


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