Physicochemical, traction and tribofilm formation properties of three octanoate-, laurate- and palmitate-anion based ionic liquids

Abstract

Three new ionic liquids with different anions and the same cation were synthesized from fatty acids through a metathesis reaction. All the ionic liquids were identified via NMR and FTIR and several properties (density, viscosity, thermal, and environmental) were measured. Traction tests were performed under different entrainment speeds (10-2000 mm/s), at slide-roll ratio (SRR) of 50% and 30 N-load, and at different temperatures (40, 60, 80 and 100 ºC) using a mini-traction machine (MTM). Tribofilm formation tests were also made in the MTM at 50 N-load, 150 mm/s of entrainment speed, at SRR of 50% and temperature of 100 ºC, for 60 minutes. This work showed that the alkyl chain length in the anion affects properties such as viscosity, toxicity, biodegradability and lubrication. Viscosity decreased with increasing alkyl chain length but only below 60ºC, at higher temperatures the viscosity values of the ionic liquids converge. The toxicity and biodegradability increased with the alkyl chain length, but these novel ionic liquids are much better from both toxicity and biodegradability points of view than the [N8881][TFSI] ionic liquid, which contains the same cation and anion not coming from fatty acids. The ionic liquids at low temperature (40 ºC) performed under elastohydrodynamic lubrication and changed to mixed lubrication at higher temperatures and decreasing speeds, according to the alkyl chain length of each anion. All ionic liquids adsorbed on the steel surfaces, and the tribofilm thickness and the kinetics of formation were different.

Two fatty acid anion-based ionic liquids - part I: Physicochemical properties and tribological behavior as neat lubricants

“…In addition, Yu et al [63] observed that longer alkyl chain makes the salt more viscous because of an increase in van der Waals interactions. However, both properties decrease in this research with the increase of the alkyl chain length of the anion, similarly to other FAILs employed in previous research works [64][65][66][67]. The differences in viscosity behavior could be explained in a similar way that what happen with surface tension [46].…”

“…Besides, the onset of temperature degradation was between 165 and 180 ºC (Table 3). Comparing these mentioned results with that of two ILs containing the same anions obtained in a previous research, it was found that thermogravimetric results are almost the same until T 50% (around 200 ºC) [64].…”

Novel fatty acid anion-based ionic liquids: Contact angle, surface tension, polarity fraction and spreading parameter

“…All these reagents were provided by Sigma-Aldrich S.A and used without further purification. These FAILs were obtained through a salt metathesis reaction, which is explained in a previous research work [53].…”

Relationships between the physical properties and biodegradability and bacteria toxicity of fatty acid-based ionic liquids

“…The fatty acid-based ionic liquids (FAILs) were synthesized by means of a salt metathesis reaction according to Battez et al [31]. The details related to their identification through 1 H and 13 C NMR and FTIR analyses can also be found in Battez et al [31] and Blanco et al [32].…”

“…The fatty acid-based ionic liquids (FAILs) were synthesized by means of a salt metathesis reaction according to Battez et al [31]. The details related to their identification through 1 H and 13 C NMR and FTIR analyses can also be found in Battez et al [31] and Blanco et al [32]. Methyltrioctylammonium bromide ionic liquid ( 97%) was employed as cation precursor and natural fatty acids: hexanoic ( 98%), octanoic ( 98%), lauric ( 98%), palmitic ( 98%), stearic ( 98%) and oleic ( 95%) acids were used as anion precursors.…”