Question: I would like to know if the dyne test can be used effectively on a vertical surface.
Answer: This is a good question. The dyne test is based on wetting (spreading) vs. beading (shrinking) on a flat, horizontal surface. You can imagine it as a balance between the gravitational force tending to spread the liquid over the surface vs. the resistance to spreading due to the surface tension of the liquid. We have had a couple of customers who test their web upside down on line while their machine is stopped — in this case, both forces work together to keep the liquid from spreading; wetting is clearly impeded, and some sort of data adjustment will be necessary.
In a vertical configuration, the bottom of the liquid swath will be strongly drawn downwards away from itself by gravity, whereas the top of the liquid swath will be drawn downwards into itself by the same force.
In brief, this configuration is far from ideal. The reaction of the fluid at the left and right sides of the liquid swath could be evaluated, but there is still an anomaly involved: the dyne test is based on receding contact angles, meaning that the behavior of a liquid on an already wetted surface is what is analyzed. In the case of a vertically positioned sample, the liquid is likely to run down the surface to an area which has not been pre-wetted. In this case, the advancing contact angle of the liquid/solid interface — rather than the receding one — comes into play. At least with regard to polymer testing, this could be a significant source of systematic error.
In summary, I do not advise this orientation. However, if no other option is available, and if you can do direct A:B testing on two surfaces that you know have identical surface energies — one test on a horizontal surface and one on a vertical one — you may be able to devise a method and a data adjustment which will provide meaningful results. But please keep in mind that, even with the data adjustment, the odds are you will not derive the same dyne level in this manner that another tester might come up with while testing in the traditional horizontal orientation.