1 Copyright © 2005 by ASME Proceedings of WTC 2005: World Tribology Conference September 12-16, Washington DC WTC2005-63221 INORGANIC FULLERENE-LIKE NANOPARTICLES AS NEW LUBRICANT ADDITIVES: A DRUG DELIVERY MECHANISM L. JOLY-POTTUZ, Ecole Centrale de Lyon, France J.M. MARTIN, University Institute of France, Ecole Centrale de Lyon F. DASSENOY, Ecole Centrale de Lyon, France C. SCHUFFENHAUER, Weizmann Institute of Science, Israel R. TENNE, Weizmann Institute of Science, Israel N. FLEISCHER, NanoMaterials, Ltd, Israel ABSTRACT When dispersed in a synthetic polyalphaolefin (PAO) base oil, inorganic fullerene-like (IF-MS 2 ) nanoparticles of metal dichalcogenides (IF-MoS 2 , IF-WS 2 , IF-NbS 2 ) lead to a significant reduction of both friction and wear under boundary lubrication. The effect of the contact pressure on the tribological properties of IF nanoparticles is particularly interesting. Results show that the higher is the pressure, the lower is the friction coefficient. The effect of the concentration shows that, even used at a low concentration (0.1%wt), IF-MS 2 is able to decrease friction (0.05) compared to base oil only (0.08). A steady state friction coefficient of 0.04 was reached with IF-WS 2 at 1%wt in PAO. Friction-induced transformation of the IF-MS 2 nanoparticles into H-MS 2 single sheets was evidenced by High Resolution Transmission Electron Microscopy (HRTEM). Some of these superimposed sheets are found in incommensurate positions, thus possibly explaining the very low friction coefficient of 0.04 obtained with IF-WS 2 . In-situ Raman spectroscopy was performed during a friction test to follow this structural modification. The lubrication mechanism of IF-MS 2 is very similar to a “drug delivery system”. A very low concentration of additives is sufficient and the activation is obtained by the opening of the nested structure, like in certain micellar structures. Furthermore, no chemical reaction is required to obtain interesting properties. Thus, fullerene-like nanoparticles are active at the very beginning of the test and even at ambient and low temperature. INTRODUCTION Today, additives used as friction modifiers and anti- wear agents are mainly organic compounds containing sulphur and phosphorous. Basically, their lubrication mechanism depends on chemical reactions, leading to the formation of some harmful compounds (radicals for example). Friction reducing properties of MoDTC have been attributed to the generation of pristine MoS 2 single sheets directly in the contact area [1]. A way to replace this additive would be to find another product which is able to produce such MS 2 sheets. Because of their unique and spheroidal morphology, fullerene-like nanoparticles of MS 2 compounds were first thought to present interesting tribological properties because of their possible rotation ability like tiny ball bearings [2]. This is not likely with the corresponding layered structure of these compounds. Moreover, their nanometric size allows them to enter easily into the contact area. Their structure, without dangling bonds, confers them a chemical inertness. Later, it was observed by TEM that most of the IF nanoparticles are actually strongly modified under the pressure and shear in the lubricated test. Ultimately, they generate MS 2 sheets with layered structure [3, 4]. Here, first we compare the tribological properties of different kinds of Inorganic fullerene-like nanoparticles (IF- WS 2 , IF-NbS 2 and IF-MoS 2 ) as additives dispersed in a PAO base oil. Second, we show new approaches (Diamond Anvil Cell and in-situ Raman spectroscopy) that can give valuable information to better understand the mechanism by which IF nanoparticles deliver the active species. This mechanism, based on the formation of MS 2 sheets [3, 4], can be compared with a “drug delivery mechanism” , a well known mechanism in pharmacology. EXPERIMENTAL IF-MoS 2 and IF-NbS 2 were synthesized according to [5] and [6], respectively. IF-WS 2 was supplied by Nanomaterial, Ltd (www.apnano.com). Proceedings of WTC2005 World Tribology Congress III September 12-16, 2005, Washington, D.C., USA WTC2005-63221