Wilhelmyplattmetoden

The Wilhelmy plate method is a technique used to measure surface tension and interfacial tension. It relies on the principle of wetting a thin plate with a liquid and measuring the force required to pull the plate away from the liquid surface.

The apparatus consists of a sensitive balance from which a thin, rectangular plate, typically made of platinum, is suspended. The plate is carefully brought into contact with the liquid surface. When the plate is just touching the surface, a force is exerted on it due to surface tension. This force is measured by the balance. As the plate is pulled away from the surface, the surface tension acts downwards, and the balance records this downward pull.

The surface tension (γ) can be calculated using the formula γ = F / (2 * (w + t)), where F is the measured force, w is the width of the plate, and t is the thickness of the plate. The term 2 * (w + t) represents the perimeter of the plate in contact with the liquid. Accurate measurement requires that the plate is perfectly clean and that the contact angle between the plate and the liquid is zero, meaning the liquid perfectly wets the plate.

The Wilhelmy plate method is a static method, meaning it measures the tension at equilibrium. It is versatile and can be used to study surface tension of liquids and interfacial tension between two immiscible liquids. It is also employed in studying the properties of surfactants and polymers at interfaces. Variations of the method exist, but the core principle of measuring the force on a wetted plate remains the same.