Wilhelmy plate

In this method, the plate is oriented perpendicular to the interface, and the force exerted on it is measured.

Based on the work of Ludwig Wilhelmy, this method finds wide use in the preparation and monitoring of Langmuir films.

The plate is often made from filter paper, glass or platinum which may be roughened to ensure complete wetting.

The force on the plate due to wetting is measured using a tensiometer or microbalance and used to calculate the surface tension (

In practice the contact angle is rarely measured; instead, either literature values are used or complete wetting (

[2] In general, surface tension may be measured with high sensitivity using very thin plates ranging in thickness from 0.1 to 0.002 mm.

The buoyancy adjustment is minimized by utilizing a thin plate and dipping it as little as feasible.

[3] If complete wetting is assumed (contact angle = 0), no correction factors are required to calculate surface tensions when using the Wilhelmy plate, unlike for a du Noüy ring.

Illustration of Wilhelmy plate method. The magnitude of the capillary force on the plate is proportional to the wetted perimeter, , and to the surface tension of the liquid-air interface.