25 / 2017-01-26 15:09:41

Space charge Formation Related to the structural relaxation of SiO2/LDPE nanocomposite

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THE addition of inorganic nanoparticles into polymers has been studied to improve the electrical properties of materials
in the past 10 years. Several papers have reported that SiO2/LDPE nanocomposites can effectively decrease space charge accumulation and DC conductivity at room temperature. However, space charge build up and suppress mechanism in nanocomposite are still not well understood. Lewis and Tanaka’s interface model distinguishes a Gouy-Chapman double layer, with a thickness of approximately 100 nm, consists of mobile positive and negative ionic charges. The common view of the two scholars is that an interfacial charge layer may exist in the nanocomposite and influence the space charge accumulation. We detected the interface charge layer in SiO2/LDPE and MgO/LDPE nanocomposites using the SAXS and AFM measurements. The results revealed that interfacial charge exist in SiO2/LDPE but not in MgO/LDPE. Although there is no obvious interface charge layer detected in the MgO/LDPE nanocomposite, the space charge properties of MgO/LDPE still significantly improved, which revealed that the interface charge is not the dominant factor influencing the dielectric properties. Carrier traps have been pointed out to play an important role in space charge accumulation in polymers and TSC provided a great deal of information about carrier traps. Experiments results showed that LDPE has a TSC peak around 60℃and the mechanical loss curve of LDPE which has a peak corresponding to the α-relaxation correspond well to the TSC peak. Space charge of LDPE at different temperatures were obtained by PEA then the sum of space charge amount showed that the space charge curve of LDPE at different temperatures still has a peak and it correspond well to the TSC and DMA peak. These results proved this point of view that space charge accumulation is associated with molecular motions. Compared with LDPE, the DMA loss peak of SiO2/LDPE was lower and shifted to higher temperature which implied that nanoparticles could restrict the movement of LDPE chain. The TSC peak appeared in LDPE is suppressed in SiO2/LDPE nanocomposite and the space charge peak correspond to TSC peak is also suppressed. These experiments results provided some evidences that the space charge suppress mechanisms of LDPE based nanocomposite has correlation with the bound effects on chain movement.