Influence of Matrix and Surfactant on Piezoelectric and Dielectric Properties of Screen-Printed BaTiO3/PVDF Composites

Abstract

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.

Keywords: characterization; composite; dielectric; fluorinated surfactant; piezoelectric; polarization; screen-printing; surface functionalization.

Figure 1

(a) Upper view of the circular capacitor; (b) real photo of the printed samples with different shapes.

Figure 2

Scheme of the deposition process.

Figure 3

Scheme of the poling experimental setup.

Figure 4

FTIR spectra of BaTiO₃ particles: (a) “None”; (b) “3F-ben”; (c) “3F-met”; (d) “3Si”.

Figure 4

FTIR spectra of BaTiO₃ particles: (a) “None”; (b) “3F-ben”; (c) “3F-met”; (d) “3Si”.

Figure 4

FTIR spectra of BaTiO₃ particles: (a) “None”; (b) “3F-ben”; (c) “3F-met”; (d) “3Si”.

Figure 5

Viscosity of different solutions as a function of shear rate: (a) PVDF–HFP and PVDF–TrFE polymers; (b) composites with 30% BaTiO₃ in PVDF–TrFE or PVDF–HFP; (c) 60% BaTiO₃ in PVDF–TrFE (with surfactants “3F-met” and “3Si”).

Figure 5

Viscosity of different solutions as a function of shear rate: (a) PVDF–HFP and PVDF–TrFE polymers; (b) composites with 30% BaTiO₃ in PVDF–TrFE or PVDF–HFP; (c) 60% BaTiO₃ in PVDF–TrFE (with surfactants “3F-met” and “3Si”).

Figure 6

SEM micrographs of composites with (a) 30% BaTiO₃ in PVDF–HFP, and (b) 30% BaTiO₃ in PVDF–TrFE.

Figure 7

SEM micrographs of cross-sections of composites with 60% BaTiO₃ (in PVDF–TrFE).

Figure 8

Broadband dielectric permittivity (${\epsilon }_{33}^{\prime }$) of (a) PVDF–HFP and PVDF–TrFE composites (30% BaTiO₃), and (b) PVDF–TrFE composites (60% BaTiO₃, surfactants “3F-met” and “3Si”).

Figure 9

Loss tangent versus frequency of the (a) PVDF–HFP and PVDF–TrFE composites (30% BaTiO₃), and (b) PVDF–TrFE composites (60% BaTiO₃ + surfactants “3F-met” and “3Si”).

Figure 10

BaTiO₃ dipole distribution within the PVDF–TrFE matrix for the formulations “3Si” (b) and “3F-ben” (a).