Molecular structural, optical analyses, and dielectric properties of PVDF/PVA-MK composites

In the present work, pure metakaolin (MK) was prepared from kaolin using the heat treatment and added different contents of MK to PVDF/PVA blend to enhance the structural, optical, and electrical properties for PVDF/PVA-MK composites. The structure analysis has been studied by X-ray diffraction. After the addition of MK, an increase in the amorphous structure was observed in the composites because the MK reduced the crystallinity related to the interaction between PVDF/PVA blend and MK. The UV–Vis absorbance, transmittance and reflectance spectra were analyzed to determine absorption coefficient, indirect energy band gap, optical absorption coefficient, diffuse reflectance, and extinction coefficient. The increase in the extinction coefficient values was demonstrated with the increase in the amount of MK associated with energy loss and the reaction between light and medium molecules. The decrease in the band-gap values was demonstrated with the increases in the amount of MK to confirm the suitability of MK as a band gap regulated optical material in different applications. The dielectric permittivity, AC conductivity, and dielectric modulus were studied in details. The values of ε′ and ε″ were increased as an increase of MK content due to the high value of MK dielectric permittivity. The \({\sigma }_{\mathrm{ac}}\) values were increased as an increase of both frequencies and the addition of MK for all samples. The lower values of \({\sigma }_{\mathrm{ac}}\) were observed at the lower frequency due to the electrode polarization effect. The M″ relaxation peaks indicate a phase transition related to the transition from long-range to short-range ionic transport.