Consistent Application of Dyne Solution with Cotton Swabs

Question: Currently, we take a Q-tip, dunk it quickly in the bottle of test fluid, then cover a small area of the sample surface and wait a couple of seconds to determine if it is a pass or fail. We believe this may be slightly inaccurate due to an inconsistent amount of solution being applied to the Q-tip. Is this a valid concern?

Answer: Your concern is legitimate. The more test fluid that is absorbed by the cotton applicator tip, the thicker the fluid film will tend to be when applied unless extreme care is taken to barely touch the swab to the surface when applying the test fluid. A thicker film will, due to gravitational forces, push itself outward, resulting in a higher (and less accurate) dyne level reading.

The best way to meter the amount of fluid applied is to use a dropper bottle to apply the fluid to the swab, and specify a given number of drops to apply. For plastic film testing, we usually limit the volume to 4 or 5 drops. Your best method will depend on how large an area you choose to test, as well as empirical feedback from the tester as to which volume is easiest to read with the best replicability.

One tip that may be helpful: I am most able to control the transfer of fluid from the swab to the surface if I hold the swab almost flat, and parallel to the surface, instead of handling it like a pencil or pen. Also, it is very important to use a light touch; bearing down with the swab could scrub off surface contaminants that affect the material’s actual surface energy. And, of course, always use a fresh swab for each test, even if it is at the same dyne level.

This technique suggests purchasing small bottles of test fluid, which will increase your cost per fluid volume, but on the other hand you should save quite a bit of fluid, so you may find there’s actually no extra cost in the long run. But keep in mind the purpose of the test is to produce accurate and repeatable results – the value that accomplishing this objective offers will pay dividends in improved product quality and consistency.

Published by

Russ Smith

Russ Smith formed Diversified Enterprises - the first business to focus specifically on applications of the dyne test - in 1986, and has served as President of the company ever since. He has over 30 years of experience in the fields of surface treatment and analysis, and deals with technical inquiries from customers worldwide on a daily basis. Russ is a member of ASTM, the Society of Plastics Engineers, the American Chemical Society, the American Society for Quality, the American Association for the Advancement of Science, and TAPPI.

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