Investigation of surface trap distribution in LDPE/SiO2 nanocomposite based on simultaneous observation of space charge and relaxation current

Abstract

In this paper, trap distribution variation in low density polyethylene (LDPE) after filled with 1 wt% nanosilica is investigated through the charge decay after corona charging with a needle-plane electrodes system. The LDPE and LDPE/SiO2 nanocomposite were firstly polarized under needle-plane electrodes system. The electrons and holes are injected through the variation of polarization of the needle. Then the surface space charge behavior and relaxation current were measured with a simultaneous measuring equipment, which overcomes the poor correlation of separate measurement. Lastly, the apparent mobility and trap distribution are evaluated based on the decay of surface space charge and relaxation current decay. It is found that the observed surface space charge and current are associated with trap distribution from 0.855 eV to 1.000 eV during decay process from 10 s to 3600 s. In LDPE/SiO2 nanocomposite, the estimated trap density of electrons and holes is more than that of LDPE in a relatively low energy range from 0.855 eV to 0.925 eV. These traps with low energy levels as transport media for carriers may be the main reason for the higher mobility of carriers in LDPE/SiO2 than LDPE, which is testified by surface space charge decay. It is also worth noting that according to the relaxation current decay, the estimated density of the relatively deep hole traps (>0.990 eV) is more than that of electron traps in LDPE, which is not observed in LDPE/SiO 2 . This is in accord with other scholar's molecular simulation result that most hole traps exist in intra-chain areas and electron traps exist in inter-chain areas, reflecting the different transportation characteristics of electrons and holes.