What Does Wilhelmy Plate Method Mean?
Wilhelmy plate method is used for measuring the surface tension of a liquid and an indirect method to measure the contact angle between a solid and liquid. The Wilhelmy plate method involves measuring force on a plate immersed vertically in the liquid. The Wilhelmy plate is a rectangular, thin plate made of iridium-platinum which has good wetting properties on contact with a liquid.
The sample is attached to a very precise balance and allowed to immerse in the liquid. The force acting on the immersed sample is measured.
Trenchlesspedia Explains Wilhelmy Plate Method
The Wilhelmy plate sample is attached to the arm of a very precise balance. A temperature controlled water bath arranged on a programmed stage moves up and immerses the sample. The stage moves down allowing the sample to leave the water. The force applied to the sample and the position of the stage is recorded. The contact angle is measured using the formula:
F L = Υwater/air cosθ - dΔρg
where, F - pulling force (measured by balance),
L - wetting length (twice the width of the sample),
Υwater/air - water surface interfacial tension with air at given temperature
θ - contact angle
d - immersed depth of sample
Δρ - density difference between water and sample
g - acceleration of gravity