Up/Down Tuning of Poly(ionic liquid)s in Aqueous Two‐Phase Systems

Abstract Thermally induced reversible up/down migration of poly(ionic liquid)s (PILs) in aqueous two‐phase systems (ATPSs) was achieved for the first time in this study. Novel ATPSs were fabricated using azobenzene (Azo)‐ and benzyl (Bn)‐modified PILs, and their upper and lower phases could be easily tuned using the grafting degree (GD) of the Azo and Bn groups. Bn‐PIL with higher GD Bn could go up into the upper phase and Azo‐PIL come down to the lower phase when the temperature increased (>65 °C); this behavior was reversed at lower temperatures. Moreover, a reversible two‐phase/single‐phase transition was realized under UV irradiation. Experimental and simulation results revealed that the difference in the hydration capacity between Bn‐PIL and Azo‐PIL accounted for their unique phase‐separation behavior. A versatile platform for fabricating ATPSs with tunable stimuli‐responsive behavior can be realized based on our findings, which can broaden their applications in the fields of smart separation systems and functional material development.