Carlo Carbone

The aim of this paper was to provide insight into the impact of matrix and surfactants on the rheology, morphology, and dielectric and piezoelectric properties of screen-printed BaTiO₃/PVDF composites. Two matrices were compared (PVDF–HFP and PVDF–TrFE), and lead-free BaTiO₃ microparticles were added in volume fractions of 30% and 60%. Here, we demonstrated that the presence of surfactants, helping to prevent phase separation, was crucial for achieving a decent screen-printing process. Fourier-transform infrared (FTIR) spectroscopy together with scanning electron microscopy (SEM) showed that the two “fluoro-benzoic acid” surfactants established stable bonds with BaTiO₃ and improved the dispersion homogeneity, while the “fluoro-silane” proved to be ineffective due to it evaporating during the functionalization process. PVDF–TrFE composites featured a more homogeneous composite layer, with fewer flaws and lower roughness, as compared with PVDF–HFP composites, and their inks were characterized by a higher viscosity. The samples were polarized in either AC or DC mode, at two different temperatures (25 °C and 80 °C). The 30% BaTiO₃ PVDF–TrFE composites with two fluorinated surfactants featured a higher value of permittivity. The choice of the surfactant did not affect the permittivity of the PVDF–HFP composites. Concerning the d₃₃ piezoelectric coefficient, experimental results pointed out that PVDF–TrFE matrices made it possible to obtain higher values, and that the best results were achieved in the absence of surfactants (or by employing the fluoro-silane). For instance, in the composites with 60% BaTiO₃ and polarized at 80 °C, a d₃₃ of 7–8 pC/N was measured, which is higher than the values reported in the literature.