Interface Trapping Effects on the Charge Transport Characteristics of LDPE/ZnO Nanocomposites

This paper intends to reveal the interface trapping effect on the charge transport characteristics of LDPE/ZnO nanocomposite by combined study of the nanocomposite structures, trap level distributions, space charge distributions, conduction current and charge mobility. Experimental results show that nanofillers in the nanocomposites significantly altered the microstructure of the polymer matrix by introducing lots of smaller spherulites and increasing the crystallinity, leading to a significant increase in the interface areas between amorphous and crystalline regions. The trap density in the nanocomposites is about 2 - 6 times that in LDPE. The traps are essentially cavities, located at the interface areas between nanofillers and polymer matrix and interface areas between amorphous and crystalline regions. A new method was proposed to evaluate the carrier mobility as a function of discharge time and trap depth from the IDC results directly. The carrier mobility of LDPE is about 4-20 times higher than that of the nanocomposites. Compared with LDPE, bulk space charge accumulation is significantly suppressed in the nanocomposites. An interesting discovery is that there is a clear correspondence between the space charge accumulation and current increase in I-t characteristics under high electric field. The study indicates that the low charge carrier mobility and space charge suppression in LDPE/ZnO nanocomposites and the I-t behavior are all closely related to the interface trapping effects in the nanocomposites.