1 Time - resolved characterization of dynamic 2 tribochemical processes for dicationic imidazolium 3 ionic liquid 4

Dynamic tribochemical processes for dicationic ionic liquid containing a germinal 14 imidazolium cation head groups bridged by a poly(ethylene glycol) and 15 bis(trifluoromethylsulfonyl)imide anion were studied using time-resolved Mechanically 16 Stimulated Gas Emission Mass-Spectrometry (MSGE-MS). In comparison with similar 17 monocationic imidazolium ionic liquids with short alkylic or long polyether side chains the 18 dicationic ionic liquid had lower coefficient of friction on Ti6Al4V alloy and smoother behaviour. 19 The analysis of volatile decomposition products suggested multiple tribochemical reactions in 20 which both anionic and cationic moieties are involved. Tribochemical degradation of cations was 21 mainly through detachment of the side and bridging chains from the imidazolium head groups. 22 Absence of volatile products containing nitrogen implies that imidazole group remained 23 unchanged. Hydrogen and water desorption were attributed to the reactions of hydrogen fluoride 24 being a product of anion degradation with titanium and titanium oxide. 25