Structural evolution of imidazolium-based poly (ionic liquid) assemblies during solvent evaporation

Poly (ionic liquid)s (PILs) with a desirable tunability in their structures and properties have promising potentials to produce a hierarchically ordered functional materials. The structural evolution of imidazolium-based PILs with different counteranions during in-situ solvent evaporation has been investigated. Small angle X-ray scattering (SAXS) and X-ray diffraction studies indicate that upon solvent evaporation, poly [C16VIm+][Br–] displays a weakly ordered lamellar morphology and finally a hexagonal perforated lamellar structure. Over a wide range of dimethyl formamide (DMF) content, however, the poly [C16VIm+][BF4–]/DMF mixture shows a lamellar structure with a tiny minority of bicontinuous cubic phase that disappears instead in the corresponding dried samples caused by the decrease in space-filling requirement for alkyl chains arrangement. For poly [C16VIm+][PF6–], there is almost no change in inner structures with solvent evaporation except a more ordered lamellar morphology observed in the dried sample. Notably, an interdigitated packing of alkyl tails dominates the lamellar sheets for all dried PIL samples. These results indicate that the design and fabrication of PIL assemblies with ordered structures can be achieved by simply changing counteranion and solvent content, which offers a feasible approach for engineering PIL-based nano-scale functional materials