Immobilized ionic liquid induced electroactive β-phase in poly(vinylidene fluoride) thin films

Ferroelectric poly(vinylidene fluoride) (PVDF) has been proposed in the past decades as an electroactive material for various applications in microelectronic devices due to its ferro/piezo/pyroelectric properties. However, fabrication of smooth PVDF thin films with a high content of beta-phase and controlled chain orientation is a long-standing problem. Here we report on the control over polymorphs of PVDF thin films by exploring the interfacial ion-dipolar interactions. The ion-dipolar interactions are provided by CF2 bonds of PVDF and imidazolium type ionic liquid immobilized onto substrates via biomimetic catecholic attachment chemistry. By simply melt crystallization of spin-coated PVDF thin films at elevated temperatures, the ferroelectric polar beta-phase with a lying-down chain orientation is formed. The thin films exhibit excellent ferro/piezoelectric properties when applying electric field due to the immobilization of ionic liquids. The results may boost the applications of PVDF in microelectronic devices.