This theoretical text provides you with a short description of the measurement principles used by the KRÜSS Tensiometers and their software LabDesk.

Surface and interfacial tension measurements

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 in 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.

Most KRÜSS 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. 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.

A further requirement is that the probe must have a very high surface energy. This is why a platinum-iridium alloy is used for the ring and roughened platinum for the plate.