Aqueous biphasic systems (ABS) can integrate multiple
unit operations
and operate under continuous mode, contributing to the development
of sustainable separation processes. Encouraged by the designer solvent
features of ionic liquids (ILs), we herein propose their use as components
of double-stimuli-responsive (temperature- and pH-driven) ABS. Resorting
to choline-alkanoate-based ILs as the pH-responsive components and
poly(propylene glycol) (PPG 400) as the thermo-responsive component,
the ABS ternary phase diagrams are determined at various temperature
(25–45 °C) and pH (3–7) conditions. While the liquid–liquid
phase diagram response to temperature obeys a lower critical solution
temperature-like behavior, the response to pH correlates with the
pK
a of the IL anion parent acid. The simultaneous
responsiveness to temperature and pH is then shown, whose results
inspire the development of customizable separation techniques as proved
with the simultaneous (one-step) separation of two dyes. By a proper
customization of the IL chemical structure and stimuli applied, ABS
may be designed to improve the performance and sustainability of separation
processes.