Study on Surface Charge Characteristics of Polyethylene/SiO2 Nano-composites Observed by Kelvin Probe Force Microscope

摘要

The study of the generation, injection and movement of electric charge in nano-dielectric polymer plays an important role in understanding the dielectric mechanism of nano-dielectric properties modification. To research the effect of different concentrations and types of nanoparticles on dielectric, hydrophilic nano-SiO₂ and modified hydrophobic nano-SiO₂ are doped at 0.5wt% and 3wt% in LDPE respectively. In order to study the microscopic charge motion characteristics of nano-dielectrics, a Kelvin probe force microscope (KPFM) based surface potential tracking experiment is performed. At the same time, surface potential data are analyzed and treated with curve fitting. Under continuous testing, it can be seen from the KPFM that the surface potential of SiO₂/LDPE disappeared much slower than the pure LDPE, and the LDPE doped with hydrophobic SiO₂ is even slower. This proves that the doping of nanoparticles reduces the conductivity of LDPE, and the hydrophobic SiO₂ has a stronger effect. Moreover, the surface potential of the LDPE doped with nano-SiO₂ still existed for over 180 minutes, and the final surface potential increases with the increasing of doping concentration. This phenomenon indicates that the charge injected into the SiO₂/LDPE nano-composite moves more slowly, and the interface area between SiO₂ and LDPE brings more traps, resulting in the charge trapped. The curve fitting results show that the surface potential attenuation is exponential and the fitting parameters of different samples are obtained. The results showed that the potential attenuation of SiO₂/LDPE is significantly slower than LDPE, and the potential attenuation of modified hydrophobic nano-SiO₂ is slower than that of hydrophilic nano-SiO₂.