Complex coacervation of polymerized ionic liquids in non-aqueous solvents

Polymerized ionic liquids (PILs) are a subset of polyelectrolytes with numerous interesting properties, including solubility in organic solvents for certain ion pairs. In our study, two oppositely charged PILs were used to form complex coacervates in different organic solvents, i.e. 2,2,2-trifluoroethanol (TFE) and hexafluoro-2-propanol (HFIP). In these two media with relatively low dielectric constants (27 for TFE, 16.7 for HFIP) compared to aqueous systems (80 for water), coacervate phase diagrams were constructed via UV-Vis and ¹⁹F-NMR spectroscopy. Notably, the critical salt concentrations required for complete miscibility were significantly different in the two solvents, while ‘positive’ tie lines—corresponding to higher concentration of small ions in the coacervate phases than in the supernatant phases—were found in both systems. This study provides insight into the effect of low dielectric solvents on complex coacervation, which has not been widely studied due to the limited solubility of most polyelectrolytes in these media.