Automatic digital tensiometers are expensive - three to four times more so than a high-precision manual tensiometer. We hope to clearly depict when an automatic digital tensiometer is not merely nice to have, but essential.
duNouy Ring and Wilhelmy Plate Techniques.
The duNouy Ring method is based on a technique developed by P. Lecomite duNouy and popularized in a paper published in 1925. In this technique a platinum ring is first submerged below the surface of a liquid. The ring is then brought up through the surface. The force necessary to do this and break the meniscus formed at the surface of the fluid is measured. This force is transformed into surface tension terms, usually dynes per cm.
The duNouy method has been used for measuring a wide range of products. It can be used for very low surface tensions, and any surface tension up to a high of 90 dynes/cm. Traditional torsion balance tensiometers are still in wide use because of their inherent precision and stability.
The Wilhelmy plate method is based on the force applied by a liquid to pull on a material immersed in that liquid. The higher the surface tension the greater the force. Wilhelmy plates are well suited for high surface tension liquids and can be used to measure changes in surface tension over time. Tensiometers based upon electronic balances are often used for Wilhelmy Plates applications. These usually provide a digital readout but have limited capability for time-based surface tension analysis.
If your requirements call for measuring only surface tension, the more basic duNouy ring tensiometer is probably the best choice. When you have very thick, high viscosity requirements, a Wilhelm Plate instrument will work.
When conducting basic surface tension tests, in normal ranges, we recommend the duNouy Ring Tensiometer.
Requirements that Point to the Need for an Automatic Tensiometer
If you have requirements for measuring surface tension which change over time, such as measuring the reaction times of surfactant, the Automatic Tensiometer is a good solution.
An automatic tensiometer has unique capabilities for determining Lamella Length, which is the amount of stretch in a liquid between the development of maximum force and the total release of a duNouy ring.
Measurements of changes in apparent surface tension or wettability of different substrates are enhanced with automated techniques.
Most automatic tensiometers have attachments that will control the temperature of the sample.
Most automatic tensiometers also perform routine duNouy Ring and Wilhelmy plate tests. These instruments also record historical results, perform statistical analyses of multiple tests, and plot test readings.
When Do You Need An Automated Solution?
A number of testing requirements clearly point to the need for an automatic tensiometer.
- Time based surface tension tests
- Measurement of Lamella Length
- Wettability analysis
- Temperature controlled samples and/or
- Continuous recording, plotting and retention of all test results
If these are part of your analysis requirements, an automatic Tensiometer is the only practical answer. The ability to conduct your routine duNouy and Wilhelmy Method tests comes as a free added benefit.
We hope this has provided some guidance for the answer to When Do I Need An Automatic Tensiometer?
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The wide range of issues involved with selection and use of laboratory test equipment frequently baffle but always interest me.
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