Electrospray induced ferroelectricity in poly(vinylidene fluoride) thin films

Abstract

Ferroelectric polymer thin films are interesting for applications in flexible and lightweight electronic equipment. Among the ferroelectric polymers, poly(vinylidene fluoride) (PVDF) possesses the highest theoretical ferroelectric moment. However, development of single-step production methods of PVDF thin films containing a significant ferroelectric moment is difficult, due to the large number of processing requirements that need to be fulfilled simultaneously: film deposition, ferroelectric β-phase formation, and dipole alignment. Nonetheless, electrospray deposition appears to be a promising method. The structure of electrospray-deposited films has been studied by infrared absorption and the ferroelectricity of the films has been determined by AFM methods and by macroscopic I–V measurements. Films prepared with solutions of 0.05 wt% PVDF in DMF consist solely of small ferroelectric β-phase crystallites embedded in amorphous phase. The formation and alignment of β-phase dipoles occur progressively during electrospray deposition because of the ion current present in electrospray. Moreover, if the non-ferroelectric α-phase is initially present in the film, it disappears progressively as a function of spray time. Thus, electrospray can provide PVDF thin films with a level of ferroelectricity depending on the spray current and on the spray time.