Investigation of the rheological and conductive properties of multi-walled carbon nanotube/polycarbonate composites by positron annihilation techniques

The microstructure, rheological and conductive properties of multi-walled carbon nanotube (MWCNT)/polycarbonate (PC) composites were investigated by positron annihilation lifetime spectroscopy, positron annihilation coincidence Doppler broadening (CDB), oscillatory rheometry and electrical resistivity for different MWCNT contents. A 10 orders of magnitude increase in electrical conductivity was achieved with very small quantities of MWCNTs. CDB was used to determine a percolation threshold value, which was in good agreement with the electrical conductivity and rheological measurements. The results showed that with increasing MWCNT content, the composites underwent a phase transition from insulating to conducting at room temperature, which was attributed to the formation of a MWCNT network. The effect of MMCNTs on the microstructure of MWCNT/PC composites has been studied by positron annihilation lifetime measurements. The results showed that the fractional free volume decreased because of the MWCNTs and the formation of conductive network. The effects of MWCNT filler on the atomic scale free volume and mechanical property of MWCNT/PC composites were also discussed.