Shear Strength and Tribological Properties of Stearic Acid Films—Part I: On Glass and Aluminum-Coated Glass

The mechanical shear strength of dry and lubricated interfaces is evaluated by measuring the frictional force during sliding of a hemispherical pin in contact with a flat slide. The solids investigated include bare glass and aluminum-coated glass and interfaces are generated from pairings of these materials. Lubrication is obtained by depositing a stearic acid Langmuir-Blodgett layer on the slide. Shear strength is measured at contact stresses ranging from ~ 0.05 to 0.8 GPa and at a sliding speed of 60 μm s⁻¹. The shear strength of dry interfaces is found to increase with contact stress, and increases slightly with aluminum film thickness. Because stearic acid adheres to glass and aluminum, the shear strength of lubricated interfaces originates from the interaction of two stearic acid layers generated from molecular redistribution over the surfaces during sliding. For lubricated interfaces, the shear strength increases nearly linearly with contact stress, in agreement with the results of earlier work. The shear strength of stearic acid is found to depend slightly on the combination of sliding materials. Lubricant durability is found to be largest in glass/glass sliding interfaces.