Albert Dato

Barium titanate (BTO) is a ferroelectric perovskite used in electronics and energy storage systems because of its high dielectric constant. Decreasing the BTO particle size was shown to increase the dielectric constant of the perovskite, which is an intriguing but contested result. We investigated this result by fabricating silicone-matrix nanocomposite specimens containing BTO particles of decreasing diameter. Furthermore, density functional theory modeling was used to understand the interactions at the BTO particle surface. Combining results from experiments and modeling indicated that polymer type, particle surface interactions, and particle surface structure can influence the dielectric properties of polymer-matrix nanocomposites containing BTO. Graphical abstract

Barium titanate (BTO) is a ferroelectric perovskite with potential in energy storage applications. Previous research suggests that BTO dielectric constant increases as nanoparticle diameter decreases. This report recounts an investigation of this relationship. Injection-molded nanocomposites of 5 vol% BTO nanoparticles incorporated in a low-density polyethylene matrix were fabricated and measured. Finite-element analysis was used to model nanocomposites of all BTO sizes and the results were compared with experimental data. Both indicated a negligible relationship between BTO diameter and dielectric constant at 5 vol%. However, a path for fabricating and testing composites of 30 vol% and higher is presented here.

Graphene can be synthesized in the gas phase using atmospheric plasmas. Gas‐phase‐synthesized graphene (GSG) possesses features that make it a promising filler material for enhancing the properties of polymers. In this study, epoxy‐matrix nanocomposites reinforced with GSG were investigated. Mixing GSG with epoxy showed that the nanomaterial effectively disperses and resists aggregation in polymer resins. Significant increases in both strength and strain at break were revealed through the tensile testing of GSG‐filled nanocomposites. In contrast, nanocomposites containing graphene nanoplatelets exhibited enhanced strength but diminished strain at break. Imaging of nanocomposite fracture surfaces by scanning electron microscopy indicated considerable matrix reinforcement by GSG. These results show that unique strengthening mechanisms exist in polymers reinforced with graphene synthesized in atmospheric plasmas.

The size dependence of the dielectric constants of barium titanate or other ferroelectric particles can be explored by embedding particles into an epoxy matrix whose dielectric constant can be measured directly. However, to extract the particle dielectric constant requires a model of the composite medium. We compare a finite element model for various volume fractions and particle arrangements to several effective medium approximations, which do not consider particle arrangement explicitly. For a fixed number of particles, the composite dielectric constant increases with the degree of agglomeration, and we relate this increase to the number of regions of enhanced electric field along the applied field between particles in an agglomerate. Additionally, even for dispersed particles, we find that the composite method of assessing the particle dielectric constant may not be effective if the particle dielectric constant is too high compared to the background medium dielectric constant.