text: The du Noüy Padday rod consists of a rod usually on the order of a few millimeters square making a small ring. The rod is often made from a composite metal material that may be roughened to ensure complete wetting at the interface. The rod is cleaned with water, alcohol and a flame or with strong acid to ensure complete removal of surfactants.  The rod is attached to a scale or balance via a thin metal hook. The Padday method uses the maximum pull force method, i.e. the maximum force due to the surface tension is recorded as the probe is first immersed ca. one mm into the solution and then slowly withdrawn from the interface. The main forces acting on a probe are the buoyancy (due to the volume of liquid displaced by the probe) and the mass of the meniscus adhering to the probe. This is an old, reliable, and well-documented technique.
  An important advantage of the maximum pull force technique is that the receding contact angle on the probe is effectively zero. The maximum pull force is obtained when the buoyancy force reaches its minimum,
  The surface tension measurement used in the Padday devices based on the du Noüy ring/maximum pull force method is explained further here:
  The force acting on the probe can be divided into two components: 
  : i) Buoyancy stemming from the volume displaced by the probe, and
  : ii) the mass of the meniscus of the liquid adhering to the probe.
  The latter is in equilibrium with the surface tension force, i.e.
  where
  :*  is the perimeter of the probe,
  :*  is the surface tension and the weight of the meniscus under the probe. In the situation considered here the volume displaced by the probe is included in the meniscus.
  :*  is the contact angle between the probe and the solution that is measured, and is negligible for the majority of solutions with Kibron’s probes.
  Thus, the force measured by the balance is given by
  where
  :*  is the force acting on the probe and
  :*  is the force due to buoyancy.
  At the point of detachment the volume of the probe immersed in the solution vanishes, and thus, also the buoyancy term. This is observed as a maximum in the force curve, which relates to the surface tension through
  The above derivation holds for ideal conditions. Non-idealities, e.g. from defect probe shape, are partly compensated in the calibration routine using a solution with known surface tension.