Noüyringsmetoden

Noüyringsmetoden, often translated as the Noüy ring method, is a widely used technique for measuring surface tension. Developed by Pierre Noüy in the early 20th century, the method relies on the force required to detach a platinum-iridium ring from the surface of a liquid.

The apparatus typically consists of a sensitive balance, a stand to hold the liquid, and a precisely shaped platinum-iridium ring. The ring is first carefully cleaned to ensure it is free from contaminants. It is then immersed in the liquid to be tested and slowly pulled upwards. As the ring is lifted, a film of liquid forms between the ring and the bulk liquid surface. The surface tension of the liquid exerts a downward force on the ring, opposing its upward movement.

The maximum force recorded just before the film breaks and the ring detaches from the surface is measured by the balance. This force, along with the dimensions of the ring, allows for the calculation of the surface tension. A correction factor is often applied to account for the shape of the liquid film and the finite radius of the ring. This method is known for its accuracy and reproducibility, making it a standard technique in both research and industrial quality control for liquids such as solutions, oils, and surfactants.