To understand how lubricants work on a molecular level, we need ways of looking into the contact between two hard solids under pressures of hundreds or thousands of atmospheres and at shear rates > 105 s–1. Sum-frequency spectroscopy and Raman scattering have been exploited for this purpose: a circular contact is formed between a prism and a sphere and lasers are focused into the small area of contact (the dark region in the centre of the Newton rings, left). Vibrational spectroscopy can tell us which organic molecules are in the contact and how they respond to pressure and shear.[1,2] A total internal reflection geometry is employed to increase signal levels and to provide greater control over the polarisation of the electric fields at the interface. The development of in situ infrared spectroscopy of lubricant films is being undertaken in collaboration with Prof. Biswas at the Indian Institute of Science in Bangalore.
1. R. Fraenkel, G. E. Butterworth and C. D. Bain "In Situ Vibrational Spectroscopy of an Organic Monolayer at the Sapphire–Quartz Interface" Journal of the American Chemical Society 1998, 120, 203–204 (DOI).
2. D. A. Beattie, S. Haydock and C. D. Bain "A Comparative Study of Confined Organic Monolayers by Raman Scattering and Sum-Frequency Spectroscopy" Vibrational Spectroscopy 2000, 24, 109–123 (DOI).
3. O. P. Khatri, C. D. Bain and S. K. Biswas "Effects of Chain Length and Heat Treatment on the Nanotribology of Alkylsilane Monolayers Self-Assembled on a Rough Aluminium Surface" Journal of Physical Chemistry B, in press (DOI).