WilhelmyPlatte

The Wilhelmy plate (Wilhelmy-Platte in German) is an experimental technique in surface chemistry for measuring liquid surface tension and wetting properties using a flat plate of known dimensions that is in contact with the liquid. The method is named after Ludwig Wilhelmy, a 19th‑century German physicist who introduced this approach.

In the standard setup, a plate is suspended from a sensitive balance and slowly immersed in the liquid. The force F required to hold or detach the plate is measured. If the liquid fully wets the plate (contact angle θ ≈ 0), the surface tension γ is given by γ = F / P, where P is the wetted perimeter of the plate (for a rectangular plate P ≈ 2(a + b)).

For nonzero contact angles, γ = F / (P cos θ). The method can also be used to study dynamic surface tension by monitoring changes in F during immersion or withdrawal, and to estimate wetting properties of solids by comparing γ with known values.

Applications include measurement of surface tension for liquids such as water, organic solvents, and surfactant solutions, as well as comparative studies of wetting on solid substrates. It is common in chemical analysis, materials science, and process engineering.

Advantages of the Wilhelmy plate method include a direct and relatively simple measurement with minimal liquid handling and fast response, particularly when the liquid fully wets the plate. Limitations include sensitivity to surface contamination, dissolution or adsorption on the plate, the need for accurate plate dimensions and perimeter, and the requirement to account for the contact angle if it deviates from zero.