Interactions occur between the molecules of a liquid and those of any liquid or gaseous substance which is not soluble in the liquid; these result the formation of an interface. Energy is required to change the form of this interface or surface. The work required to change the shape of a given surface is known as the interfacial or surface tension.
Tensiometers determine the surface or interfacial tension with the help of an optimally wettable probe suspended from a precision balance; this is either a ring or a plate (for example, a DeNoeuy Ring or Wilhelmy Plate). A height-adjustable sample carrier is used to bring the liquid to be measured into contact with the probe. A force acts on the balance as soon as the probe touches the surface. If the length of the probe is known (circumference of ring or length of plate) the force measured can be used to calculate the interfacial or surface tension. As a further requirement is that the probe must have a very high surface energy. Therefore a platinum-iridium alloy is used for the ring and roughened platinum for the plate.
This method is not only used for tension measurement but also for studies of the contact angle (wilhemy plate). At this, the surface of the plate is exposed to liquids, as a result a meniscus is created at the contact point. This causes engergy between the plate and liquids due wetting. As soon as the plate is completely wetted, the surface tension can be directly measured with the plate's geometry.
Heraeus offers the suitable measurement equipment for surface tension, e.g. Wilhelmy Plates, de Noeuy rings or precious metal capillary tubes. All rings and plates are annealed without residue to ensure a clean demarcation of the samples. This demonstrates the special properties of our material which gets through this procedure again and again.
