In situ observation of adsorbed fatty acid films using surface plasmon resonance

• The use of SPR measurements for monitoring adsorption processes under lubricant shearing conditions was first demonstrated.
• SPR measurements technique has a high potential for in-situ observation of the kinetics of adsorption processes.
• The amount of inflow of adsorption molecules into the contact regions is an important factor in promoting the growth of adsorbed films.

This paper presents an example of the application of surface plasmon resonance (SPR) measurements to tribological studies. Using a common configuration of SPR, i.e., the Kretschmann attenuated total reflection configuration, the kinetic characteristics of fatty acid additive adsorption on a gold surface were observed in situ and in real time under shearing. These tests demonstrated that the amount of inflow of adsorption molecules into the contact regions, which is determined by the shear rate and the concentration of stearic acid concentrations, is an important factor in promoting the growth of adsorbed films.