Ionic-liquid-induced ferroelectric polarization in poly(vinylidene fluoride) thin films

Thin films of ferroelectric β-phase poly(vinylidene fluoride) (PVDF) were spin-coated from a solution that contained small amounts of the ionic liquid (IL) 1-ethyl-3-methylimidazolium nitrate. A remanent polarization of 60 mC/m2 and a quasi-static pyroelectric coefficient of 19 μC/m2K at 30 °C were observed in the films. It is suggested that the IL promotes the formation of the β phase through dipolar interactions between PVDF chain-molecules and the IL. The dipolar interactions are identified as Coulomb attraction between hydrogen atoms in PVDF chains and anions in IL. The strong crystallinity increase is probably caused by the same dipolar interaction as well.