Electrical properties and conduction mechanism in carboxyl-functionalized multiwalled carbon nanotubes/poly(vinyl alcohol) composites

The electrical properties of carboxyl-functionalized multiwalled carbon nanotubes (MWCNT-COOH)/poly(vinyl alcohol) (PVA) nanocomposites prepared by solution casting method were investigated by employing dielectric relaxation spectroscopy in the broad frequency range of 0.1 Hz to 1 MHz and temperatures from 123 to 423 K (i.e.-150 to 150 A degrees C). Using dc conductivity and critical frequency (f (c)) obtained from the dc to ac transition, the percolation (I broken vertical bar(c)) was found to be 0.12 vol.%. The actual aspect ratio of the nanotubes in the nanocomposites was calculated using the excluded volume theory as well as Garboczi model, and it was observed that the solution casting method did not significantly alter the aspect ratio of MWCNT-COOH. In addition, the contact resistance (R (c)) between the conductive nanotubes was found to be 10(8) a"broken vertical bar. The temperature dependence of conductivity of these nanocomposites was studied. The conductivity decreased exponentially with the temperature decreasing from 423 to 313 K. The corresponding curve was explained by the mechanism of hopping conductivity. For the temperature range of 303-123 K, a gradual decrease of conductivity was observed. This was explained with the fluctuation-induced tunneling of electrons between neighboring carbon nanotubes.