“My duNouy ring kept falling off the arm hook when attempting to immerse it into a high-viscosity sample.”
This is the first time any of us at CSC Scientific recall being presented with such a dilemma. This client was using a single arm tensiometer to do surface tension measurements
The ring, on a single-arm tensiometer is attached by putting the top through a hook as shown in the photo. It is clear that when dealing with a high-viscosity sample, you would have to push the ring through it with your finger -- a somewhat cumbersome process.
This problem is solved with our interfacial tensiometer, in which the ring is affixed to the stationary vertical arm by way of a rigid joint. Thus, when the ring is inserted into the sample, the vertical arm pushes it down, breaking the surface.
Given this, from now on we will recommend only the interfacial model for high-viscosity samples.
In the course of developing a solution to this problem, I delved into the relationships of surface tension and viscosity. My next discourse on surface tension will attempt to interpret these relationships.
Let us know of your experiences with duNouy ring tests on high viscosity samples.
As always a totally perplexed,
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By Art Gatenby