Synthesis and modification of silver and BaTiO3 particles as fillers for polymeric composites with high dielectric constant

There is an increasing demand of high permittivity (high-k) materials due to the rapid development of the electronic industry and the need of more efficient energy storage devices. The combination of dissimilar components in composites is expected to be an effective approach to better dielectric materials. The inclusion of high-k particles, such as Ag and BaTiO3, in a polymeric matrix can significantly increase the dielectric constant while preserving the flexibility and the high breakdown voltage typical of polymers. The combination of high-permittivity and large breakdown fields is a fundamental requirement to store electrostatic energy with high density. Ferroelectric BaTiO3 nanoparticles (50-100 nm) were obtained by a hydrothermal-like method starting from cheap inorganic precursors (BaCl2 and TiCl4). The size of the particles was tailored by changing the precursor concentration. Silver particles (20-200 nm) were synthesized by a solvothermal method using ethylene glycol as a solvent and AgNO3 as a precursor and adding polyvinylpyrrolidone (PVP) as growth modifier to control the particle size. The nature of the inclusion-polymer interface has a strong impact on the dispersion of the inorganic particles and the dielectric properties of the resultant composite. The compatibility between the two phases was improved by functionalizing the particles with specific coupling molecules, such as silane-based compounds. As a further strategy to improve the dielectric properties of the composite, the particles were coated with a thin TiO2 shell, which has a dielectric constant intermediate between the filler and the polymer matrix and thus realizes a more homogeneous distribution of the electric field.