This work is focused on the correlation between several physical properties (kinematic viscosity, viscosity index, refractive index, density and water solubility) and biodegradability and bacteria toxicity of a family of ionic liquids synthesized from fatty acids as anion precursor (FAILs): methyltrioctylammonium hexanoate [N 8881 ][C 6:0 ], methyltrioctylammonium octanoate [N 8881 ][C 8:0 ], methyltrioctylammonium laurate [N 8881 ][C 12:0 ], methyltrioctylammonium palmitate [N 8881 ][C 16:0 ], methyltrioctylammonium stearate [N 8881 ][C 18:0 ] and methyltrioctylammonium oleate [N 8881 ][C 18:1 ]. To that end, new values of these physical properties, biodegradability and bacteria toxicity were determined, although literature data for the [N 8881 ][C 8:0 ], [N 8881 ][C 12:0 ] and [N 8881 ][C 16:0 ] FAILs were also needed. It was found a good linear relationship (r 2 > 0.90) between the biodegradability index (BOD 5 /COD) and the logarithm of kinematic viscosity, refractive index and water solubility for the saturated FAILs. Besides, the toxicity on both Vibrio fischeri and Escherichia Coli can be successfully predicted using the logarithm of kinematic viscosity and viscosity index. Therefore, kinematic viscosity, which is an essential parameter for a lubricant, is the most promising physical property to estimate both biodegradability and bacteria toxicity of a family of ionic liquids. The double bond in the structure of the unsaturated FAIL ([N 8881 ][C 18:1 ]) is responsible for the worsening of the linear dependence between physical and environmental properties.

This research deals with the tribological behavior and corrosion performance of three novel fatty acid anion-based ionic liquids (FAILs): methyltrioctylammonium hexanoate ([N8,8,8,1][C6:0]), methyltrioctylammonium octadecanoate ([N8,8,8,1][C18:0]) and methyltrioctylammonium octadec-9-enoate ([N8,8,8,1][C18:1]), employed for the first time as neat lubricant with five different material pairs: steel–steel, steel–aluminum alloy, steel–bronze, steel–cast iron and steel–tungsten carbide. These novel substances were previously obtained from fatty acids via metathesis reactions, identified structurally via NMR (nuclear magnetic resonance) and FTIR (Fourier-transform infrared spectroscopy) techniques, and then characterized from a physicochemical (density, water solubility, viscosity, viscosity index and refractive index) and environmental (bacterial toxicity and biodegradability) points of view. The corrosion behavior of the three FAILs was studied by exposure at room temperature, while friction and wear tests were performed with a reciprocating ball-on-disc configuration. The main results and conclusions obtained were: (1) Corrosion in the presence of the three FAILs is observed only on the bronze surface; (2) All FAILs presented similar tribological behavior as lubricants for each tested material pair; (3) XPS (X-ray photoelectron spectroscopy) analysis indicated that the surface behavior of the three FAILs in each material pair was similar, with low chemical interaction with the surfaces.

This study investigates the use of an ionic liquid obtained from fatty acids (FAIL) as an additive at 2 wt.% in two different base oils: a mineral oil (M1) and a polyol ester (E1). Physicochemical characterization of the base oil–FAIL blends confirmed the miscibility of the FAIL in the base oils. The addition of the FAIL hardly changed the density of the base oils and the viscosity slightly increased at lower temperatures. The tribological performance of the base oils and their blends with the FAIL was determined using three different tests: Stribeck curve determination and tribofilm formation tests, both under sliding/rolling motion, and reciprocating wear tests. The M1 + FAIL blend showed the lowest friction values under the mixed lubrication regime due to its higher viscosity, while the E1 + FAIL showed the lowest friction values under the elastohydrodynamic lubrication regime, which may well have been due to its higher polarity. Only the E1 + FAIL blend outperformed the antiwear behavior of the base oil, probably because it has better chemical affinity (higher polarity) for the metallic surface. SEM images showed that the predominant wear mechanism was adhesive-type with plastic deformation and XPS studies proved that the presence of increasing amounts of organic oxygen on the wear scar caused better antiwear performance when the E1 + FAIL blend was used.

This work reports thermal stability, traction and tribofilm formation properties of three 12 fatty acid-derived ionic liquids (FAILs) and evaluates the influence of the chemical structure of 13 the anion on the properties indicated above. The results indicated that thermal stability of the 14 FAILs is related with the chemical structure of the anion (longer alkyl chain length increases 15 thermal stability and the presence of double bond decreases it). At high temperatures and low 16 speeds, the [N8,8,8,1][C6:0] led to the lowest traction values and the [N8,8,8,1][C18:1] had the highest 17 ones. All FAILs reacted with the steel surfaces creating a tribofilm, that increased with time.