Widening the Stimuli-Responsiveness of Aqueous Biphasic Systems by Changing the Ionic Liquid Cation Basicity

Herein we demonstrate the formation of new stimuli-responsive aqueous biphasic systems (ABS), able to respond simultaneously to temperature and pH, or just to one stimulus, therefore allowing the design of more sustainable separation processes. This dual behavior is achieved with ABS formed by mono- or dicationic protic ionic liquids as phase-forming components, being defined by the ionic liquid cation chemical structure or its basicity. While ABS comprising monocationic ionic liquids only respond to the effect of temperature, systems comprising dicationic ionic liquids are simultaneously affected by both temperature and pH variations. Dicationic ionic liquids are here identified as the key to unlock a double response to stimuli, which is due to the presence of two pKa values afforded by the cation. The reported findings contribute to increase the customizability of double stimuli-responsive ABS based on ionic liquids, whose development was up to date limited to ionic liquids bearing pH-responsive anions, opening the door towards the development of more sustainable separation processes.