Liquid surface tension: EXP100120

This device is used to measure the surface tension coefficient using the ring method (also known as the du Nouÿ ring method) for fluids with small and average surfactant concentrations (water, hot water, oil, alcohol, etc.). A horizontal ring, a few millimetres thick, is suspended from the end of a dynamometer. The ring is then immersed in the liquid that completely wets it, before being made to emerge. A meniscus is then formed inside and outside of the ring perimeter. The value displayed on the dynamometer allows you to find the surface tension value. This device is equipped with two suspended rings, two dynamometers and a lab jack.

DU NOUY RING METHOD FOR WATER SURFACE TENSION

A metal ring, of known radius, fastened to a dynamometer, is immersed in a liquid that wets it completely. A force, known as the tensile force, must be overcome at the vicinity of the free surface to pull this ring out of the liquid. A small crystal container filled with water is placed on a lift holder, and the dynamometer is suspended above the liquid. The ring is suspended at the bottom end of the dynamometer, and is immersed completely by raising the lab jack. The holder is then lowered slowly to extract the ring from the liquid. The dynamometer is elongated under the effect of the surface tension forces. The tensile force is read on the dynamometer when the ring is pulled out of the liquid, to determine the surface tension value.

COMPARING THE SURFACE TENSION OF DIFFERENT FLUIDS

With 0.1 N and 0.2 N dynamometers, you can measure the surface tension value of a large number of fluids with a varying degree of surface tension: water, saltwater, hot water, soapy water, oil, alcohol, etc. The idea is that students observe the differences in accuracy of implementation of their test protocol.

DEPENDENCY OF THE SURFACE IN CONTACT WITH THE FLUID

We supply two rings for this experiment. As surface voltage value is dependent on the surface in contact with the fluid, it is possible to compare surface tension values for the same fluid and two different ring diameters.

SUBJECTS APPROACHED

»»Surface energy
»»Surface tension measurement
»»Du Nouÿ ring method

NECESSARY EQUIPMENT