Aggregation and phase equilibria of fluorinated ionic liquids

• Published in: Journal of molecular liquids 2019-07, Vol.285, p.386-396
• Main Authors: Vieira, Nicole S.M., Bastos, Joana C., Hermida-Merino, Carolina, Pastoriza-Gallego, María J., Rebelo, Luís P.N., Piñeiro, Manuel M., Araújo, João M.M., Pereiro, Ana B.
• Format: Article
• Language: English
• Subjects: Fluorinated ionic liquids; Liquid-liquid phase equilibria; Self-aggregation; Solubility; Surface activity
• ISSN: 0167-7322; 1873-3166
• DOI: 10.1016/j.molliq.2019.04.086

In this work a specific family of ionic liquids, denominated fluorinated ionic liquids, with fluorine tags equal or longer than four carbon atoms, are fully characterized in order to understand their solubility and self-aggregation in aqueous solutions. The numerous combinations between cations and anions make these compounds a feasible option for the replacement of traditional and toxic surfactants used in the industrial and biomedical field. In this work, the increment of both hydrogenated and fluorinated side chain lengths, the influence of the cation headgroup (imidazolium and cholinium) as well as the difference between perfluorobutanesulfonate and perfluoropentanoate anions were studied. The liquid-liquid phase equilibria of fluorinated ionic liquids based on the perfluorobutanesulfonate anion with water were carried out. The self-aggregation behaviour of the different fluorinated ionic liquids in aqueous solutions was also determined using conductimetric titration, surface tension measurements and transmission electron microscopy. Several thermodynamic and surface parameters were obtained and used to discuss the aggregation process. These novel characterized fluorinated ionic liquids demonstrate an improved surface activity and aggregation behaviour, driven essentially by the increment of both hydrogenated and fluorinated chain lengths. [Display omitted] •The liquid-liquid phase equilibria of the binary systems FILs with water were measured using a visual method.•The self-aggregation behaviour of FILs in aqueous solution was determined by conductimetric titration and surface tension.•FILs structures and sizes were analysed by transmission electron microscopy.•The increment of alkyl chain length decreases the solubility of FILs in aqueous solutions.•Higher surfactant behaviour is achieved with FILs with longer hydrogenated and fluorinated chain lengths.