Alkylated fullerene as lubricant additive in paraffin oil for steel/steel contacts

An alkylated fullerene which bears three eicosyl chains (3,4,5-C20C60, 1) was synthesized via [3 + 2] cycloaddition. At 25°C where the aliphatic chains are in the crystalline state, 1 exhibits a moderately improved solubility in paraffin oil compared to pristine C60. At 80°C which is well-above the chain melting temperature (Tc), a significant solubility increase was observed. Upon cooling to 25°C, suspension containing plate-like aggregates composed of lamellar subunits form, which can be stable for several days. Applications of 1 as a lubricant additive in paraffin oil (PO) for steel/steel contacts both below and above Tc have been investigated in detail. It was found that the addition of 1.0 wt% 1 to PO can reduce the friction coefficient by ∼24% at 25°C. Moderate reduction of the friction coefficient at 90°C was also observed. Analysis on the worn surfaces revealed a pronounced antiwear property of 1 by reducing the areas of the worn surfaces and smoothing the scuffing. Our results show that alkylated fullerenes can be potentially used as a new generation of lubricant additives. Finally, the lubrication mechanisms of 1 at different temperatures were discussed.