The first additives that improve the tribological properties of ionic liquids were designed. They were evaluated by a ballon-flat type tribo-test under reciprocating motion. Tetraalkylammonium and tetraalkylphosphonium salts of N-protected aspartic acid was dissolved in 1-alkyl-3-methylimidzolium bis(trifluoromethylsulfonyl)imide. They prevented wear remarkably and reduced friction considerably. The salt of N-protected glutamic acid prevented wear but did not reduce friction under the conditions we have evaluated. A new model of boundary film composed of liquid clathrate structure is proposed herein.Ionic liquids are unique fluids that possess non-flammability, non-volatility, and outstanding thermo-oxidative stability. These properties are desirable for lubricating fluids, especially for lubricants used under extreme conditions. Since ionic liquids are composed of anion and cation, variation in their structure is estimated more than one million compounds.1 The tribological properties of certain ionic liquids have been reported. 2 In our previous work, 1,3-dialkylimidazolium-derived ionic liquids were found to exhibit comparable tribological properties to the conventional synthetic lubricants such as perfluoropolyethers. 3 We also pointed out the importance of additives that improve the tribological properties of ionic liquids. However, ionic liquids are strange solvents; they hardly dissolve the conventional lubricant additives. Simple carboxylic acids improved the tribological properties of dialkylimidazorium-derived ionic liquids. 4 However, these carboxylic acids are volatile and corrosive. Based on our concept of molecular design of lubricant additives, 5 chemical modification of carboxylic acid by introduction of certain functional group was examined. Here, we wish to report molecular design of the first additives that improve anti-wear properties of ionic liquids.In our preliminary work, we found that dicarboxylic acids such as succinic and glutaric acid reduced friction of 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide (BIMI-TFSI), while adipic acid did not. Solubility of these simple acids in BMIM-TFSI still remains the problem. These simple compounds are volatile and corrosive in fact, however the relation between chemical structure and the tribological properties are of interest. Recently, aspartic acid-and glutamic acid-derived ionic liquids were developed.6-8 The structural features of them are functionalized dicarboxylic acid obtained from natural resources. The ionic structure is beneficial to dissolve them into ionic liquids. Thus, we synthesized trialkylammonium and trialkylphosphonium salts of these amino acids. The free amino group was protected by benzyl or acetyl group to improve the stability. Structure of the designed additives is shown in Figure 1. Samples for the tribo-test were prepared by dissolving the additive in BIMI-TFSI at the concentration of 10 mmol kg À1 .The tribological properties were obtained using a ball-onflat type tribo-tester under reciprocating motion a...

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Tribological properties of organic sulphides in esters were examined under boundary conditions. Magnification of wear by sulphides was observed in unsaturated esters. A dumb-bell-shaped wear scar, composed of a 'central area' and a 'border area', was found as an intermediate of wear growth. The 'border area' then expanded, resulting in a large wear scar. An induction period was observed before the generation of the 'border area'. Influences of additive concentration on the induction period were also observed. Surface analyses of worn surfaces revealed that organic oxides, sulphides (unreacted additive) and sulphoxides are present in the boundary film. Influence of auto-oxidation of the base oil on wear mechanism was proposed.