High Energy Density Nanocomposites Based on Surface-Modified BaTiO₃ and a Ferroelectric Polymer

Abstract

The dielectric permittivity and electric breakdown strength of nanocomposites comprising poly(vinylidene fluoride-co-hexafluoro propylene) and phosphonic acid surface-modified BaTiO(3) nanoparticles have been investigated as a function of the volume fraction of nanoparticles. The mode of binding of pentafluorobenzylphosphonic acid on the BaTiO(3) particles was investigated using infrared and (31)P solid-state nuclear magnetic resonance spectroscopy, and the phosphonic acid was found to form well ordered, tightly bound monolayers. The effective permittivity of nanocomposites with low volume fractions (<50%) was in good agreement with standard theoretical models, with a maximum relative permittivity of 35. However, for nanoparticle volume fractions of greater than 50%, the effective permittivity was observed to decrease with increasing nanoparticle volume fraction, and this was correlated with an increase in porosity of the spin-coated nanocomposite films. The dielectric breakdown strength was also found to decrease with increasing volume fraction of the BaTiO(3) nanoparticles, with an abrupt decrease observed around 10% and a gradual decrease for volume fractions of 20-50%. Comparison of these results with model calculations, using statistical particle packing simulations and effective medium theory for the permittivity and breakdown strength, indicates the important roles of nanoparticle percolation and porosity of the nanocomposites on the dielectric properties. The measured energy density at a field strength of 164 V/mum, well below the breakdown strength, increased to a value of 3.2 J/cm(3) as the nanoparticle volume fraction is increased to 50%, roughly in line with the trend of the permittivity. The calculated maximum energy densities indicate maximal extractable energy (7-8 J/cm(3) at 1 kHz) for two different particle volume fractions, as a result of the interplay of the dependencies of permittivity and breakdown strength on volume fraction.

Effect of silane coupling agent on the morphology, structure, and properties of poly(vinylidene fluoride–trifluoroethylene)/BaTiO3 composites

“…Surface functionalization of CaCO 3 with a fluorinated alkoxysilane led to PVDF nanocomposites with enhanced filler dispersion, better thermal stability and improved gas barrier [30], while a commercial organo-silane coated ZnO only slightly increased the storage modulus of a P(VDFTrFE) based nanocomposite versus uncoated ZnO, with no influence on the dispersion state of the filler or on the crystallinity of the matrix [31]. High permittivity nanocomposite films were fabricated by embedding, into VDF-based polymer matrices, BaTiO 3 particles that were surface modified with fluorinated phosphonic acid [32], dopamine [27,33], organofunctional titanates with long alkyl chains [34,35], aminopropyl triethoxy silane [25], or surface hydroxylated by refluxing in aqueous H 2 O 2 [36,37]. Furthermore, in a different approach, BaTiO 3 nanoparticles were generated in situ in a PVDF-g-HEMA copolymer, in which the -OH group of the HEMA units acted as a bridge with the nanoparticles surface, obtaining high dielectric constant, although the dielectric losses also increased with BaTiO 3 concentration [38].…”

Short-term breakdown and long-term failure in nanodielectrics: a review

“…NANOCOMPOSITES present a series of unique properties, such as electrics [1][2][3], mechanics [4][5], optics [6][7] and magnetics [8,9], due to nanoparticles with a giant specific surface area, quantum size effect and the special interface between particles and polymer matrix. Nanodielectrics have attracted a great attention since the first experimental data were reported publicly in 2002 [10][11].…”

The effect of processing conditions on the morphology, thermomechanical, dielectric, and piezoelectric properties of P(VDF-TrFE)/BaTiO3 composites

“…Although the piezoelectric coefficient d 33 of conventional BaTiO 3 is lower than that of PZT, a large effort is lately taking place in fabricating high-performance BaTiO 3 [19]. In addition to this, polymer/BaTiO 3 composites are also of great interest for the fabrication of high-relative permittivity materials for, e.g., embedded capacitors [20][21][22][23][24]. For polymer/BaTiO 3 composites the reported absolute values for d 33 are usually between 1 and 30 pC/N [6,8,25,26] (the sign depending on the polarization conditions in the case of piezoelectric polymer matrices), although a d 33 higher than 50 pC/N was reported for a PVDF/BaTiO 3 composite [27].…”