Influence of hydrophilic/hydrophobic protic ionic liquids (PILs) on the poly(vinylidene fluoride) (PVDF-ionic liquid) membrane properties

In this study, we investigate the effect of protic ionic liquids (PILs) on the properties of poly(vinylidene fluoride)/protic ionic liquids (PVDF/PIL) composite membranes made by solvent casting. The morphology, polymer phase, crystallinity, proton conductivities and mechanical properties were determined according to the nature and quantities of PIL added. Independently of the ionic liquids nature among EtPy][HSO4], [Py][HSO4], [(Octyl)(3)NH][HSO4] and [(Octyl)(3)NH][H2PO4], we observed the crystallization of PVDF into more stable electroactive phases (beta and gamma). Furthermore, the presence of PIL decreased the elastic modulus and modified the crystallization kinetics, as indicated by the size of the spherulitic microstructures. Proton conductivity results suggest the predominance of the Grotthuss-type conduction mechanism for all PVDF/PIL composites membranes supplied by the amphoteric anions, HSO4- and H2PO4-. Finally, the higher stable conductivities observed for hydrated membranes with [(Octyl)(3)NH][HSO4] evidenced that the Grotthuss mechanism is favored by amphiphilic cation associated with the stronger hydrogen-bonded network of the [HSO4](-)anion.