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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 [N8881][C6:0], methyltrioctylammonium octanoate [N8881][C8:0], methyltrioctylammonium laurate [N8881][C12:0], methyltrioctylammonium palmitate [N8881][C16:0], methyltrioctylammonium stearate [N8881][C18:0] and methyltrioctylammonium oleate [N8881][C18:1]. To that end, new values of these physical properties, biodegradability and bacteria toxicity were determined, although literature data for the [N8881][C8:0], [N8881][C12:0] and [N8881][C16:0] FAILs were also needed. It was found a good linear relationship (r2 > 0.90) between the biodegradability index (BOD5/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 ([N8881][C18:1]) is responsible for the worsening of the linear dependence between physical and environmental properties.

This work deals with the determination of several wetting properties (contact angle, surface tension, polarity fraction and spreading parameter) of six novel fatty acid anion-based ionic liquids (FAILs): methyltrioctylammonium hexanoate [N8881][C6:0], methyltrioctylammonium octanoate [N8881][C8:0], methyltrioctylammonium laurate [N8881][C12:0], methyltrioctylammonium palmitate [N8881][C16:0], methyltrioctylammonium stearate [N8881][C18:0] and methyltrioctylammonium oleate [N8881][C18:1]. Surface tension was determined at temperatures from 293 to 333 K, exhibiting a linear decrease within the temperature range. Contact angle measurements were performed on five different surfaces (steel, aluminum, tungsten carbide, cast iron and bronze) using 3 test liquids (water, diiodomethane and ethylenglycol) and each of the synthesized FAILs. Polarity fraction (PF) and the spreading parameter (SP) were calculated in order to gain a deeper understanding of wetting characteristics of these FAILs. Despite the similarity of the obtained results with all FAILs and surfaces, [N8881][C6:0] and [N8881][C8:0] with both cast iron and bronze surfaces were the best surface-FAIL combinations regarding wettability.