First-principles investigations of the dielectric properties of polypropylene/metal-oxide interfaces

摘要

Nanoscale-resolved dielectric properties of polypropylene/metal-oxide (alumina, PbTiO_3) interfaces and of the corresponding surfaces are investigated via first-principles calculations. In order to ascertain the locality of the atomically resolved permittivity profiles, we propose a simple procedure to directly evaluate the real-space decay length of nonlocal effects in the dielectric susceptibility. Based on this decay length, the microscopic dielectric response is derived by using a convolution of rectangular and Gaussian filters as the averaging weight function. This procedure converges quickly to the bulk values in slabs of only moderate thicknesses, while providing atomic-layer-resolved permittivity profiles even in the presence of significant relaxations and surface structure. Our results show that i the surface-induced and interface-induced modifications to the dielectric permittivity in polymer/metal-oxide composites are localized to only a few atomic layers; ii the interface effects are mainly confined to the metal-oxide side; and iii metal-oxide particles larger than a few nanometers should retain the average macroscopic value of their bulk dielectric permittivities.