High energy density nanocomposites based on surface-modified BaTiO(3) and a ferroelectric polymer

Area of Science:

• Materials Science
• Polymer Science
• Nanotechnology

Background:

• Poly(vinylidene fluoride-co-hexafluoro propylene) (PVDF-HFP) is a versatile polymer for dielectric applications.
• Barium titanate (BaTiO3) nanoparticles are known for their high dielectric permittivity.
• Surface modification of nanoparticles is crucial for enhancing compatibility and properties in polymer nanocomposites.

Purpose of the Study:

• To investigate the dielectric permittivity and electric breakdown strength of PVDF-HFP/BaTiO3 nanocomposites.
• To understand the influence of phosphonic acid surface modification on BaTiO3 nanoparticles.
• To correlate the dielectric properties with nanoparticle volume fraction, porosity, and theoretical models.

Main Methods:

• Synthesis and characterization of phosphonic acid surface-modified BaTiO3 nanoparticles.
• Preparation of PVDF-HFP/BaTiO3 nanocomposite films using spin-coating.
• Measurement of dielectric permittivity and electric breakdown strength as a function of BaTiO3 volume fraction.
• Analysis using infrared and (31)P solid-state nuclear magnetic resonance spectroscopy.
• Comparison with theoretical models including statistical particle packing and effective medium theory.

Main Results:

• Well-ordered, tightly bound monolayers of pentafluorobenzylphosphonic acid were formed on BaTiO3 particles.
• Effective permittivity agreed with models for <50% nanoparticle loading, reaching a maximum relative permittivity of 35.
• Permittivity decreased above 50% loading, correlating with increased film porosity.
• Dielectric breakdown strength decreased with increasing BaTiO3 content, with an abrupt drop around 10%.
• Measured energy density increased with nanoparticle loading, reaching 3.2 J/cm³ at 50% loading.

Conclusions:

• Nanoparticle percolation and film porosity significantly influence the dielectric properties of PVDF-HFP/BaTiO3 nanocomposites.
• Theoretical models provide good agreement for permittivity at lower loadings but require consideration of porosity at higher loadings.
• Optimal energy density (7-8 J/cm³ at 1 kHz) is achievable through a balance of permittivity and breakdown strength, dependent on nanoparticle volume fraction.