The Wilhelmy method: a critical and practical review

A brief history of the Wilhelmy technique for surface tension and contact angle measurements introduces the equation and the methods necessary to apply this modern and automatic procedure correctly. Many simple practices may avoid systematic errors and allow reliable results to be obtained for both quantities. The paper analyzes not only simple runs that is, applications to standard shapes such as cylinders and parallelepipeds, rigid, non-porous samples immersed in probe liquids of low viscosity - but also non-simple runs - that is, applications to non-standard samples such as disk-shaped samples, porous and flexible samples, planar samples with different contact angles on their two opposite faces, and to the case of more viscous fluids. Many experimental details such as the size ratio of specimens to the liquid container may be extremely important; their role and the history of discussion about these topics are reviewed and discussed herein. Also, the possible determination of contact angles other than the usual advancing and receding ones is addressed.