Noüy

Noüy is a surname associated with the Noüy–Du Noüy ring method, a historically important technique for measuring the surface tension of liquids. The method and the related apparatus, commonly called the Du Noüy ring or Noüy balance, were developed in the early 20th century by French researchers to quantify the cohesive forces at a liquid’s surface. In the method, a circular ring of platinum–iridium is briefly submerged at the liquid surface and then withdrawn with a controlled, quasi-static motion. The force exerted on the ring increases as the ring detaches and peaks at a maximum, from which the surface tension is calculated using a geometric correction for the ring. The basic relation is sigma ≈ F_max / (2πR), with refinements to account for the ring’s shape and wetting.

The Noüy–Du Noüy approach was widely used for many decades and remains referenced in historical discussions of surface-tension measurement. It is most effective for liquids with moderate to high surface tension and when rapid measurements are not required. The method has limitations, including sensitivity to contact-line hysteresis, impurities, and the speed of withdrawal, which can affect accuracy. Over time, other techniques such as the Wilhelmy plate method and pendant-drop methods have complemented or supplanted it in many laboratories, but the Noüy method remains part of the foundational literature of surface science.