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

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-SiO
₂
and modified hydrophobic nano-SiO
₂
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 SiO
₂
/LDPE disappeared much slower than the pure LDPE, and the LDPE doped with hydrophobic SiO
₂
is even slower. This proves that the doping of nanoparticles reduces the conductivity of LDPE, and the hydrophobic SiO
₂
has a stronger effect. Moreover, the surface potential of the LDPE doped with nano-SiO
₂
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 SiO
₂
/LDPE nano-composite moves more slowly, and the interface area between SiO
₂
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 SiO
₂
/LDPE is significantly slower than LDPE, and the potential attenuation of modified hydrophobic nano-SiO
₂
is slower than that of hydrophilic nano-SiO
₂
.