after Pt coating. The samples were fractured
at the cryogenic condition.
The morphology of the O2 plasma etching samples were
observed by the Hitachi S-4800 at 5 kV accelerating voltage.
Before the SEM measurements with O2 etching, the PC in
the PC/MWNT composites was degraded selectively by O2
plasma etching for 5 min. Also, the etched samples were conductively
coated by using the Pt.
Mechanical Properties. The mechanical properties of the
PC/MWNT composites were investigated using an universal
testing machine (Instron 4467). Tensile test was performed
according to the ASTM D638. The speed of cross-head
movement for tensile test was 5.0 mm/min, and 7 specimens
were measured and averaged.
Results and Discussion
Electrical Properties. Figure 1 shows the electrical conductivity
of the PC/MWNT composites with the MWNT
content. For the PC/MWNT composites at 0.5 wt% MWNT
content, the electrical conductivity shows about 10-10 S/cm.
For the PC/MWNT composites at 1.5 and 2.5 wt% MWNT
content, the electrical conductivity increases dramatically
and shows about 10-3 and 10-2 S/cm, respectively, which is
considered to be a satisfactory results of the ESD materials.
This increase of the electrical conductivity suggests the formation
of the interconnected structure of the MWNT in the
PC/MWNT composites. Therefore, the percolation threshold
of the PC/MWNT composites could be considered at about
1.5~2.5 wt% MWNT content. Similar results were reported
by Pötschke et al.8 for the PC/MWNT composites by electrical
conductivity and rheological measurements, respectively.