In-Contact IR Spectroscopy of Hydrocarbon Lubricants

This paper reviews the application of infrared (IR) spectroscopy to in-contact lubrication studies, details improvements to the method and reports initial results from the study of a simple hydrocarbon fluid. IR spectra have been taken from the Hertzian region of a sliding contact lubricated by poly-α-olefin fluids. Single reflection sampling was used with a spot size of 100 μm square. The spectral range was limited to the CH stretch region of 3100--2700 cm⁻¹. The results show that it is possible to obtain good quality IR spectra from hydrocarbon films of less than 50 nm. Spectra sampled from the contact zone show peak intensity changes, frequency shifts and shape changes. Analysis of these results indicate that in the high pressure region there is an increase in gauche defects in the alkyl chain implying a more globular molecule with a lower volume but higher energy. In thin lubricant films (<100 nm) there is evidence of fluid structuring close to the metal surface.