Measurement of surface tension. Methodology.
When depositing the ink on the surface, its behavior must be observed. If in less than 2 seconds the ink retracts and forms pockets or drops separately, it means that the surface tension of the ink is higher than that of the surface of the material.
It will be necessary to repeat the test with lower surface tension test ink, as many times as necessary until shrinkage does not occur.
The surface tension value of the surface will be a value between the ink of the penultimate test -in which retraction still occurred- and that of the last one, in which the ink no longer retracted. Depending on the difference in surface tension between the samples, a more or less precise measurement will be obtained.
Surface tension of the ink
higher than the surface
Surface tension of the ink
lower than the surface
An enlarged schematic series of the behavior of ink deposited on the surface. As the surface tension of the test ink approaches that of the surface, the droplets become less well defined (lower angle of tangency).
The surface tension value of the surface will be a value between the ink of the penultimate test -in which retraction still occurred- and that of the last one, in which the ink no longer retracted. Depending on the difference in surface tension between the samples, a more or less precise measurement will be obtained.
Measurement tests in one direction or another depending on the first marker used
It is appropriate to use a medium value test ink or pen (eg 38 dynes/cm) for the first test. If the trace remains adhered without retraction for approx. 2 seconds, the surface energy of the material has a value equal to or greater than the surface tension of the liquid.
If there has been no retraction, the pen or test ink of the next higher value is applied and the observation is repeated until a retraction occurs within the next 2 seconds.
If, on the other hand, the application of the 38 dyne/cm test pen/ink has caused shrinkage within 2 seconds, the test must be repeated with the next lower value until the shrinkage no longer occurs.
If the passage from non-retraction to retraction or vice versa occurs with values of eg 36 and 38 dynes/cm, it can be determined that the surface energy of the material tested has a value between 36 and 38 dynes/cm.
