Tribology of Self-assembled monolayers (SAMs)
(a) Tribology of PFPE overcoated SAMs
Perfluoropolyether (PFPE) is the traditional lubricant used in Hard-Disk Drives (HDD). In the present study we have formed ultra-thin layers of PFPE onto different SAMs using dip-coating technique. PFPE layer of few nanometers thickness has shown greater improvement in wear durability when coated onto reactive SAMs such as APTMS (aminopropyltrimethoxysilane) and GPTMS (glycidoxypropyltrimethoxysilane) and marginal improvement when coated onto OTS (octadecyltrichlorosilane) SAM.
Fig: Variation of coefficient of friction with respect to number of sliding cycles for bare Si, Si/OTS, Si/APTMS/PFPE (thermally treated) and Si/GPTMS/PFPE-as lubricated.
Fig: Average wear durability data of three SAM surfaces and bare Si, with and without PFPE overcoat and after thermal treatment.
N. Satyanarayana, S. K. Sinha, M. P. Srinivasan, Friction and wear life evaluation of silane based self assembled monolayers on silicon surface, 2005, Life-Cycle Tribology, Elsevier (Eds. D. Dowson, M. Priest and A. Neville) Tribology and Interface Engineering Series, No. 48, Elsevier, pp. 821-826. N. Satyanarayana and S. K. Sinha, 2005, Tribology of PFPE overcoated self –assembled monolayers deposited on silicon surfaces, Journal of Physics D: Applied Physics, Vol. 38 (18), pp. 3512-3522.
N. Satyanarayana, N. N. Gosvami, S. K. Sinha and M. P. Srinivasan, Friction, adhesion and wear durability of an ultra-thin PFPE-coated 3-Glycidoxypropyltrimethoxy silane self-assembled monolayer on a Si surface, Philosophical Magazine, 87 (22) (2007) 3209-3227.
N. Satyanarayana, S. K. Sinha and M. P. Srinivasan, Tribology of ultra-thin self assembled films on Si - the role of PFPE as a top mobile layer, in The Role of Surfactants in Tribology (Eds. Kash Mittal and Girma Biresaw), Marcel Dekker publishers, USA, 2008, 111-132.