In-Contact Molecular Spectroscopy of Liquid Lubricant Films

Abstract

AbstractThe primary role of a lubricant is to control the friction and wear of rubbing surfaces to optimize the operation of a component by forming an interfacial film separating the surfaces. Lubrication research seeks to develop new lubricant formulations and to optimize component life and performance. To do this, we must understand the mechanisms of film formation and film properties and the way these relate to operating conditions. In many engineering components, the lubricant film is subjected to severe mechanical and thermal stresses as it passes through the loaded zone. These severe conditions can result in molecular alignment or conformational change and the formation of new chemical species, which will impact the lubrication performance of the fluid. The lubricant response within the contact is often transient and thus has proved difficult to study by conventional surface analytical methods. One alternative is to replace one of the surfaces by a transparent window and use molecular microspectroscopy (infrared or Raman) to analyze the film within the contact zone formed during rubbing. This article reviews the development and application of in-contact molecular spectroscopy for the study of lubricant properties within the rubbing interface for both conventional and biolubrication systems. This technique has been used to study molecular conformation, chemical composition, and pressure distribution in the high-pressure region of the contact zone. However, challenges remain, including detecting very thin films, obtaining depth profile information, and applying these methods more generally to biotribology.