Time-Resolved Characterization of Dynamic Tribochemical Processes for Dicationic Imidazolium Ionic Liquid

Abstract

Dynamic tribochemical processes for dicationic ionic liquid containing a geminal imidazolium cation head group bridged by a poly(ethylene glycol) and a bis(trifluoromethylsulfonyl)imide anion were studied using time-resolved mechanically stimulated gas emission mass-spectrometry (MSGE-MS). In comparison with similar monocationic imidazolium ionic liquids with short alkyl or long polyether side chains, the dicationic ionic liquid had a lower coefficient of friction on Ti6Al4V alloy and smoother behavior. The analysis of volatile decomposition products suggested multiple tribochemical reactions in which both anionic and cationic moieties are involved. The tribochemical degradation of cations was mainly through the detachment of the side and bridging chains from the imidazolium head groups. The absence of volatile products containing nitrogen implies that the imidazole group remained unchanged. Hydrogen and water desorption were attributed to the reactions of hydrogen fluoride being a product of anion degradation with titanium and titanium oxide, respectively.

Interfacial Structure and Boundary Lubrication of a Dicationic Ionic Liquid

“…valence ratio 2:1) are particularly favourable for tribological applications because of their high decomposition temperature 15,16 and good anti-wear performance, especially at higher temperatures. [17][18][19][20][21][22][23] While several studies have measured the lubrication response of 1:1 ionic liquids in the boundary regime, [11][12][13][24][25][26] the friction response of nanoconfined ionic liquids with ions of higher valencies remains largely unexplored. 20 The structure of nano-scale films of 2:1 ionic liquids might be expected to differ from that of 1:1 ionic liquids, and this should -in turn -lead to variation in the dynamic properties.…”

“…These favorable traits are leading to incorporation of ionic liquids in many technological directions, and here we focus on their increasing use as lubricants. In particular, it has been demonstrated that dicationic ionic liquids (with monovalent anion, i.e., valence ratio 2:1) are particularly favorable for tribological applications because of their high decomposition temperature , and good antiwear performance, especially at higher temperatures. − While several studies have measured the lubrication response of 1:1 ionic liquids in the boundary regime, − ,− the friction response of nanoconfined ionic liquids with ions of higher valencies remains largely unexplored . The structure of nanoscale films of 2:1 ionic liquids might be expected to differ from that of 1:1 ionic liquids, and this should–in turn–lead to variation in the dynamic properties.…”

Tribochemically driven dehydrogenation of undoped sodium alanate under room temperature

“…Such behaviour is typical for depleting emission sources. 34 The driving forces for such gas emission must be directly linked to mechanical action. In contrast, the emission of H 2 first leapt down to a certain non-zero value and then continued to decay for thousands of seconds forming a characteristic trail (Fig.…”

“…The gas composition and the emission rates were determined using a previously developed statistical matrix method. [32][33][34] If not stated otherwise, each test was carried out on a pristine surface zone.…”

“…The analysis of emission dynamics, or behavioural analysis, is a useful tool for the interpretation of intrinsically non-stationary MSGE-MS signals, especially when a large uncertainty about the precursors composition exists. 29,[32][33][34]39,40 It is based on a simple concept that if the mass-spectrometer signals arise from the same precursor their time series must show correlated behaviours. Then, the whole mass spectrum can be broken down into several groups in such a way that within each group signals are correlated.…”