Preparation of β-Phase Poly(vinylidene fluoride) Films on Aluminum Substrate with the Addition of Hydrated Metal Salts.

Abstract

Poly(vinylidene fluoride) (PVDF) is one of the most studied polymers that exhibits piezoelectric and ferroelectric properties. PVDF crystallizes into four different forms, namely α, β, γ, and δ phases. Generally, the nonpolar α phase, as a replacement for the polar β phase with the most superior ferroelectric and piezoelectric properties, is formed from the precursor melt and solution. Here, we report a method for the preparation of β-phase-dominant PVDF thin films by doping PVDF solution with a metal hydrated salt, such as Co(NO₃)₂·6H₂O, without any stretching procedure. The crystal structure of the film was analyzed using X-ray diffraction -2 scanning and Fourier transform infrared spectroscopy. The morphology of the film was observed using a field emission-scanning electron microscope. To determine the frequency dependence of dielectric properties, an LCR meter was used in the range of 50 Hz to 1 MHz. The crystalline phase and morphology of the electrostatic spray-deposited PVDF films depended on the chemical additive. Our results show that the addition of a metal hydrated salt can induce an in situ poling effect, consequently facilitating the preferred dipole orientation in the electrostatically sprayed PVDF films.