A transition of interface characteristics in LDPE/Al₂O₃ nanocomposites by permittivity simulation

This paper reveals an interface transition characteristics in LDPE/Al₂O₃ nanocomposites. A nonlinear variation of dielectric permittivity in nanocomposites is closely related to the interface characteristics, such as the effective thickness, the volume fraction, and the relative permittivity. The interface with a low relative permittivity is defined as a phase between nanoparticle and polymer matrix. After that, the effective permittivities of the nanocomposites are calculated by the three-phase models. The linear model which considers the interface volume by Monte Carlo calculation indicated a significant increase of interface volume fraction at low loadings, which decreased the permittivity. However, it failed to fit the permittivity at high loadings. The interface power law (IPL) model considering the interface overlap and the shape and orientation of particle is difficult to fit the measured data, particularly at low loadings. It seems that neither of the models can well fit the measured data. However, through comparison of the two models, the permittivity behaviors in low and high loading regions can be understood. The improved model with power law relation is likely useful for explaining the reduced permittivity at low loadings, while a revised IPL model could locally agree with the increased permittivity at high loadings. In light of the comparisons, it can be inferred that the reduction of ϵ_r at low loadings is ascribed to the large interface volume (low permittivity), and the enhancement of ϵ_r at high loadings is caused by the nanoparticles. A transition of interface characteristics is summarized, which is responsible for the change of dielectric properties.