Photo- and thermo-regulated phase inversion of poly(ionic liquid) aqueous two-phase systems via host–guest interaction

Smart aqueous two-phase systems (ATPS) have aroused tremendous interests in view of their tunable phase behaviors under various stimuli, and found many potential applications in the domain of separation. Here, poly(ionic liquid)s (PILs), functionalized by benzyl (Bn) and azophenyl (Azo) groups, were prepared through a post-synthesis modification strategy. The as-fabricated ATPSs composing of Azo-PIL and Bn-PIL exhibited a photo- and thermo-responsive two-phase to one-phase transition. However, when the host molecule cucurbituril[8] urea (CB[8]) was introduced, the as-developed PIL-based ATPSs underwent a reversible upper and lower phases inversion behavior, which could be tuned through light irradiation or heating treatment. The study revealed that both the grafting degree (GD) of Azo/Bn groups and the feeding ratio of CB[8] played a critical role in this switchable phase inversion behavior. In addition, the sensitive hydration ability of functional PILs to external stimuli accounted for the phase inversion behavior of ATPSs. Thereby, our finding offers a novel platform for adjusting the phase separation behaviors of ATPSs via host–guest interaction.