Space Charge in Low-density Polyethylene /micro-SiO2 composite and Low-density Polyethylene/ nano-SiOx composite with different metal electrode pairs

Nano-SiO_x and micro-SiO₂ particles were homogeneously dispersed in low-density polyethylene with a method of double-solution mixture. Both kinds of the composites were sputtered with Au and Ag on both surfaces as electrodes, respectively. Space charge in the composites was investigated with pulsed electro-acoustic method (PEA). It is shown that space charge distribution in the sample with different metal electrode pairs relates with the electrode polarity. The amount of hetero-polarity space charge in pure LDPE after being electrically prestressed with Au(+)~Ag(-) electrode pair is greater than that with Au(-)~Ag(+) electrode pair. However, homo-polarity space charge appears in the microcomposite after being electrically prestressed with either Au(+)~Ag(-) or Au(-)~Ag(+) electrode pair, and the amount of space charge increases with micro-SiO₂ content. It also could be seen that the amount of homo-polarity space charge in the microcomposite with Au(-)_~Ag(+) electrode pair is greater than that with Au(+)_~Ag(-) electrode pair. With electrically prestressing, hetero-polarity space charge appears in the nanocomposite with either Au(+)~Ag(-)or Au(-)~Ag(+) electrode pair and the amount of space charge increases with nano-SiO_x content. In addition, the amount of space charge in the nanocomposite with Au(-)~Ag(+) electrode pair is lower than that with Au(+)~Ag(-) electrode pair. The space charge distribution difference in all samples with different electrode pairs has close relation to electron and (or) hole injection efficiency of different electrode material, as well as charge trapping and detrapping process in the interfaces of the samples.