WETTABILITY OF GOLD

Experiments were run to determine the inherent wettability of gold by water. Measurements in pure steam at 101° gave a contact angle on gold of about 65° after 23,648 hr of continuous condensation. Radiotracer studies with oleic acid added to the refluxing water showed 0.209 monolayer on filmwise copper and 0.013-0.015 monolayer ou dropwise gold, indicating that the nonwetting behavior of gold is not caused by organic contamination. The average contact angle on freshly electropolished gold surfaces was found to be 62.6 ± 3.4°. Heating experiments in quartz apparatus showed three sources of erroneously low contact angles that could readily be present in this type of experiment: (1) inorganic contamination of the surface; (2) surface roughness; and (3) equilibrium not established with water vapor. Cumulative evidence indicates that the equilibrium contact angle of water on a clean, smooth gold surface is between 60 and 65°.