Probing micro-scale charge migration of polycrystalline polypropylene under high temperatures

Dynamic charge transport in polymer materials is fundamental to improve insulation performance. However, it is challenging to understand migration mechanisms at the nanoscale in polymer composites under high temperatures. Herein, polypropylene (PP) films by solution crystallization are fabricated. We use Kelvin probe force microscopy (KPFM) to explore the charge migration of PP polycrystalline microregions. The accumulation and dissipation rate obey the exponential law. Charge injection barrier of α-PP is lower than that of β-PP under normal conditions, which is mainly influenced by the surface conductivity. The charge transport rate enhances with the field strength. By constructing the heating system, the migration rate is found to increase with temperature. Furthermore, the irregular structure of β phase introduces more shallow traps, promoting charge transport at high temperatures. Charge migration states of two phases tend to be consistent above 100 ℃. An in-situ micro-region dielectric constant testing method is proposed. The dielectric constant of β phase is slightly higher. Specifically, its reverse increase beyond 100 °C is primarily attributed to interface polarization and the enhancement of dipole orientation. The observation aligns well with bulk experiments. This study provides crucial insights into the microregion charge behavior of polymer dielectrics at high temperatures.