Figure 18. 32 shows a drop of a wetting liquid and a drop of a nonwetting liquid sitting on a horizontal solid surface and surrounded by air. Show that, for both drops, the relationship between the contact angle and the magnitudes of the cohesive and adhesive forces exerted on a particle of liquid at the gas-liquid-solid junction is \(2 \sin \left(\theta_{c} / 2\right)=F_{\text {cohesive }} / F_{\text {adhesive }}\). Assume that the surface is smooth and clean, the liquid contains no impurities, and the contact angle is not influenced by the gas.

Data from Figure 18. 32

Transcribed Image Text:

(a) Liquid wets surface (b) Liquid does not wet surface points along bisector of liquid wedge Fcohesive cohesive Fo cohesive particle at junction Fadhes adhesive points perpendicular to solid surface Vector sum must point perpendicular to liquid surface (or particle would move along surface). adhesive