| 초록 |
Composites of multiwalled carbon nanotube (MWCNT)-poly (methyl methacrylate) (PMMA) were synthesized to study electrical properties and applications such as electromagnetic interference shielding and electrostatic charge storage materials. MWCNTs were synthesized by chemical vapor deposition method. Various weight concentrations of MWCNTs were homogeneously dispersed in PMMA matrix using high power sonication to prepare free-standing film. The SEM, TEM, and XPS were used to study homogeneity and structure of the composites. The DC conductivity(σDC) of composites at room temperatures increased as MWCNT concentration increased, showing typical percolation behavior with percolation threshold (pc) at ~ 0.4 wt.% of MWCNTs. Temperature dependence of σDC [σDC(T)] were measured in the range of 0.3 K ~ 300 K to study charge transport mechanism in the composites. We propose that low temperature metallic behavior in σDC(T) originated from the formation of one-dimensional conducting MWCNT networks in insulating PMMA matrix. The σDC(T) of the composites with MWCNT concentrations above pc were compared with that of the composites below pc. AC conductivity (σAC) was also measured in the frequency range of 10 Hz ~ 2 MHz and in the temperature range of 77 K ~ 300 K, in which we observed the percolation behavior for the systems. We observed the different frequency dependence of σAC for the composites above and below pc. Electromagnetic interference shielding efficiency (EMI SE) was measured in the range of 50 MHz ~ 13.5 GHz. AC dielectric constant was also measured to examine capability of antistatic materials. |
