June 2009

Digital Automated Surface Tensiometer Model 710

Last month we discussed surface tension and the various ways that it can be measured. We discussed the traditional Wilhelmy plate and Du Noüy ring methods, the pendant drop method that we have been using with our DROPimage Advanced software for the past ten years, and several other methods. We also discussed a novel approach that is based on the Du Noüy method but uses a rod in lieu of a ring. This approach is called the Du Noüy-Padday Rod Pull Method¹. It's only fitting that this month we announce a new product which is based on this method.

In our implementation of this method, a small-diameter metal probe or rod is used in lieu of a ring. A high sensitivity microbalance measures the force required to pull the probe from the test liquid. This method does not require as much volume as the ring method, setup time is much easier, and measurements can be taken in fewer than 30 seconds. Calibration of a Du Noüy-Padday tensiometer is accomplished using a liquid with a known surface tension, such as water. The method is highly repeatable offering superior sensitivity and a fast measurement cycle. Instruments based on this method typically are much more affordable than traditional ring and plate tools, a correction for buoyancy is not required (it is for the ring and plate methods), and setup is simpler. The diameter of the rod is really not important -- as long as the instrument is recalibrated when changing to a new rod. Lastly, the Du Noüy-Padday method works well with viscous liquids such as paints, oils, and polymers -- liquids that the ring and plate methods cannot accommodate.

Accordingly, we are pleased to announce the new ramé-hart Model 710 DAS (Digital Automated Surface) Tensiometer. This remarkable new product employs a small probe (DyneProbe) that is affixed to a low-noise Kibron microscale. The test liquid (3ml but as little as 50µL is required) is dispensed into a cup (DyneCup) which sits on a moving platform. The cup is raised to allow the probe to submerge. As the cup is lowered, the maximum force exerted on probe by the liquid is measured and used to calculate the actual surface tension in mN/m. Accuracy and sensitivity are each less than 0.01 mN/m. And the surface tension range is 10-100 mN/m.

DAS Tensiometer Instrument

This laboratory quality instrument is portable and compact measuring 12 x 3.2 x 6.5 inches, weighing about 5 lbs, and featuring a 12V rechargeable battery allowing it to be used in the lab, classroom, or in the field, even outdoors. This tool is ideal for remote water quality testing and monitoring applications. A change in surface tension can immediately indicate the presence of solvents, oils, detergents, and other contaminants.

The unit can run for 24 hours on a single charge. A plug-in power supply is included as well as a starter set of DyneProbes, Dynecups, user documentation, one year warranty and priority support, and lifetime technical support. Consumables are now available at our online store (www.ramehartstore.com).  

DAS Tensiometer Console

The system is controlled via a handheld console. Calibration is simple and measurements are taken with the push of a single button. The plug-and-play system is easy to learn and operate. No special training is required. 

If you have any questions about the DAS Tensiometer, or would like to purchase a unit, please contact us.

¹ J Chem Soc, Far Trans I, 71(10), 1919-1931 (1974).

If you visit our website, www.ramehart.com, you will see that it has recently been overhauled. We have cleaned up and reorganized our pages. Each of our goniometers and tensiometers now has its own page. We've improved the layout and color scheme. We have updated some of the images and will update more of them in the future. Our glossary page has been enhanced and expanded and our new Model 710 DAS Tensiometer has been added.

Many of the changes and improvements are the result of feedback we have received from current and future customers like you. Thank you. Should you have any comments or suggestions regarding our website as it is presently, we would greatly appreciate your input. As always thank you for your business -- we greatly appreciate it.