Evaluating Work of Adhesion by Adhering Liquids to and Then Peeling Them from Solids Using a Wilhelmy Tensiometer

In this work, the adhesion energies between liquids and solids have been evaluated using a tensiometer. Vertically oriented specimens of hydrophobic fluoropolymer or hydrophilic glass were immersed into a reservoir containing water or hexadecane. After a meniscus formed, the reservoir was raised or lowered to either adhere or peel the liquid from the solid. The measured force and distance were used to estimate work of wetting or adhesion. For the partially wetting fluoropolymer, liquids debonded adhesively. Accordingly, the mechanical work done per unit area was less than the surface energy of the liquids. For the completely wetting glass, liquids debonded cohesively and the work equaled the liquid surface energy. The Young Dupré equation overestimated the mechanically measured work. Simple thermodynamic equations derived from capillary forces better predicted the measured adhesion energies. Similarities between this tensiometer test and peel tests used for rubbery adhesives are discussed.