Effects of gas or vapor adsorption on adhesion, friction, and wear of solid interfaces

The adsorption of vapor molecules plays an important role in countless fields and is increasingly realized to be critical in tribology, which encompasses adhesion, friction, and wear of surfaces. This feature article reviews experimental methods for quantifying gas and vapor adsorption on flat solid surfaces under equilibrium conditions (ambient pressure and temperature) as well as the effects of these adsorbates on the adhesion, friction, and wear of various materials. Particular attention is given to species that are present in the ambient environment such as water (humidity) and organic vapors. These adsorbed species can have drastic yet varied influences on tribology depending on the surface chemistry of materials. Despite prolonged and ubiquitous observations in a broad range of materials and vapors, a fundamental understanding of the effect of adsorbed gases and vapors on the adhesion, friction, and wear of surfaces has begun only recently through surface-sensitive characterization.