Boundary lubrication capabilities of alkylsilane monolayer self-assembled on aluminium as investigated using FTIR spectroscopy and nanotribometry

In pursuing the boundary lubrication tribology of aluminium, we first explore the change in chain mobility and conformational order of alkylsilane monolayer self-assembled on aluminium surface with different chain length using grazing angle FTIR spectroscopy. In tribology, a point on a surface rubbing against another surface is subjected to contact heating and cooling till next contact. We thus track conformational order as monolayers are subjected to heating and explore reversibility on cooling back. We report here the friction generated in sliding the monolayer against a 2 mm diameter steel ball in a ball on disc arrangement in the 25–100 mN load and 1 mm/s velocity under dry conditions. The friction at the commencement of sliding is found to correlate directly with conformational order of the molecule which is varied by changing the chain length and heat treatment temperature. We find this friction to vary linearly with full width half maxima (FWHM) which is an expression of chain mobility and packing density. The initial coefficient of friction is independent of normal load but the dynamic friction which evolves with sliding is not, although the change in dynamic coefficient of friction with normal load does relate qualitatively with the a priori conformational order of the monolayers.