Morphology and dielectric investigations of hydrated-halt P(VDF-HFP) membranes

Abstract

This study focuses on a preparation and characterization of hydrated-salt membranes based on the blend of poly(vinylidene fluoride-hexafluoropropylene) [P(VDF-HFP)] and magnesium chloride (MgCl2⋅6H2O). The membranes with MgCl2⋅6H2O concentration of 0-4 wt% were prepared by solution casting technique. An elemental composition of the prepared samples was analyzed using energy dispersive x-ray spectroscopy (EDS). The surface morphology and pore size of these membranes were investigated by scanning electron microscopy (SEM). Surface roughness of the as-received membranes was evaluated by atomic force microscopy (AFM). The degree of the crystallinity and phase structures of the P(VDF-HFP) membranes were analyzed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). The dielectric and the electrical conductivity of all samples were measured in a range of 1-105 Hz. The SEM and AFM images revealed that the formation of the microporous P(VDF-HFP) membranes was controllable by the adjustment of MgCl2⋅6H2O content. The surface roughness, pore size and ionic conductivity of the as-received membranes increased with MgCl2⋅6H2O concentration. The dielectric constant reached its maximum value of about 25 at 3.5 wt% of MgCl2⋅6H2O. The XRD results showed that the mixture of MgCl2⋅6H2O salt led to a decrease in the degree of crystallinity. However, the salt-loaded P(VDF-HFP) enhanced the fraction of an electroactive β-phase up to 84% and this was confirmed by the FTIR results. This pointed out that the hydrated-salt P(VDF-HFP) membranes had a potential in new applications such as energy harvesting area.