Impact of synthesis temperature on structure of carbon nanotubes and morphological and electrical characterization of their polymeric nanocomposites

Abstract

Carbon nanotubes (CNTs) were synthesized by chemical vapor deposition technique at a broad range of temperatures, i.e. 550°C to 950°C (at 100°C intervals). CNTs were synthesized by flowing source and carrier gases (ethane, argon, and hydrogen) over Fe catalyst in a quartz tubular reactor. CNTs were melt mixed with a polyvinylidene fluoride (PVDF) matrix in a miniature mixer. The resulting nanocomposites were then compression molded, and electrically and morphologically characterized. Moreover, a wide range of characterization techniques were employed to obtain detailed information about the physical and morphological characteristics of CNTs. It was surprisingly observed that, despite the ascending trend of powder conductivity with the synthesis temperature, the nanocomposites made with (CNT)650°C had significantly lower percolation threshold (around 0.4wt.%) and higher electromagnetic interference shielding (20.3dB over the X-band for 1.1mm thickness) compared to the other temperatures. The characterization of nanofillers showed that the synthesis yield and quality of (CNT)650°C were highly superior to the other types of CNTs. At 850°C and 950°C, most of the synthesized carbonaceous materials formed graphitic structures around the sintered catalyst particles. It was also observed that the dispersion state of (CNT)650°C within the PVDF matrix was much better than that of CNTs synthesized at the other temperatures. Superior electrical properties of (CNT)650°C nanocomposites can be attributed to a combination of high synthesis yield, low diameter and decent quality of CNTs coupled with good state of dispersion within the PVDF matrix.