Wilhelmylevymenetelmällä

Wilhelmylevymenetelmällä, often translated as the "Wilhelmy plate method," is a technique used to measure surface tension and interfacial tension. This method relies on the principle of measuring the force required to pull a thin plate, typically made of platinum or a similar inert material, from a liquid surface. The plate is suspended from a sensitive balance, and as it is brought into contact with the liquid, a film of the liquid adheres to it. The force exerted by this adhering liquid film is then measured.

The Wilhelmy plate is usually positioned vertically. When it touches the surface of the liquid, the surface tension of the liquid exerts a downward pull on the plate. This pull is equal to the product of the surface tension coefficient, the perimeter of the plate in contact with the liquid, and the cosine of the contact angle. By accurately measuring this force using the balance and knowing the dimensions of the plate and the contact angle (often assumed to be zero for hydrophilic surfaces), the surface tension can be calculated. Interfacial tension can be measured similarly by immersing the plate in the interface between two immiscible liquids. This method is widely used in research and industry for characterization of liquids, surfactants, and wetting properties.