Thin poly(ionic liquid) and poly(vinylidene fluoride) blend films with ferro- and piezo-electric polar γ-crystals

Ferro- and piezo-electric poly(vinylidene fluoride) (PVDF) thin film is reported to be obtained by using a poly(ionic liquid) (PIL) [poly(2-(dimethylamino)ethyl methacrylate) methyl chloride quaternary salt] through solution route. The short range interactions between localized cationic ions of PIL and polar >CF₂ of PVDF are responsible for modified polar γ-PVDF (T₃GT₃Ḡ) formation. Modification in chain conformation of PVDF is confirmed by FTIR, XRD, and DSC studies suggesting the miscible PVDF–PIL (PPIL) blend. Up to 40 wt % loading of PIL in PVDF matrix enhances relative intensity of γ-phase up to 50% in the entire crystalline phase. The P-E hysteresis loop of PVDF-PIL blends at 25 wt % PIL loading (PPIL-25) thin film at sweep voltage of ±50 V shows excellent ferroelectric property with nearly saturated high remnant polarization ∼6.0 µC cm⁻² owing to large proportion of γ-PVDF. However, non-polar pure PVDF thin film shows unsaturated hysteresis loop with 1.4 µC cm⁻² remnant polarization. The operation voltage decreases effectively because of the polar γ-phase formation in PPIL blended film. High-sensitivity piezo-response force microscopy shows electromechanical switching property at low voltages in PPIL-25 thin films through local switching measurements, making them potentially suitable as ferroelectric tunnel barriers.