Hopping conduction in “pure” polypropylene

Abstract

A recently developed theory of steady‐state conduction in high‐density polyethylene is applied to “pure” polypropylene (PP) in the temperature range 50–93°C. Morphological changes occur in PP, including a disordered‐amorphous to monoclinic‐amorphous transition between 50 and 80°C, where, with increasing temperature T, free volume increases, and decreases with decreasing amorphous fraction. The latter competing processes lead to large increases in hopping site separation, λ, in the transition region, followed either by saturation or a maximum in λ vs. T. We speculate that segmental and/or main chain molecular motions lower apparent activation energies, are “pinned“ by applied field, and impeded by dangling bonds in regions surrounding the surfaces of crystallites. Our analysis is semi‐quantitative only, because the latter mechanisms have not been adequately quantified, and the relative contributions of each are unknown. Measurements were carried out on heated and cooled disordered‐amorphous, and 106°C, 17‐h annealed, 43% crystalline samples. Hopping distances, obtained from measured current vs. applied field characteristics, ranged from 1.2 to 5.2 nm. Apparent activation energies up to 1.80 eV were obtained from In (I/T) vs. (1/T) plots. Remarkable plateaus in the temperature range of the transition were observed in these plots, implying some carrier conduction with near zero activation energy. Possible explanations for the latter, and the electronic nature of the carriers are given. X‐ray and density flotation measurements enabled crystallinity determinations. © 1994 John Wiley & Sons, Inc.

Nanoparticle, Size, Shape, and Interfacial Effects on Leakage Current Density, Permittivity, and Breakdown Strength of Metal Oxide−Polyolefin Nanocomposites: Experiment and Theory

“…In nanocomposites that have very large contrasts in relative permittivities between host and guest materials, large disparities in the electric fields within the constituent phases occurs, , thus preventing the simultaneous realization of maximum energy densities for both constituents . For the present nanocomposites, however, the largest achieved energy density (as high as 9.4 J/cm 3 ) is observed for BaTiO 3 − iso PP composites, which have the largest materials permittivity ratio of ∼522:1.…”