Influence of carbon-nanotube diameters on composite dielectric properties

The dielectric properties of polymethylmetacrylate (PMMA) composites filled with CVD made multiwalled carbon nanotubes (MWCNT) of different mean outer diameters (d ∼ 9 nm and 12–14 nm) were investigated in the temperature range from 300 to 420 K and in a wide frequency range (20 Hz to 1 MHz). Below the percolation threshold the temperature dependence of the complex dielectric permittivity of the investigated composites is mainly caused by β relaxation in pure PMMA matrix and the dielectric permittivity is found to be higher in composites with thicker nanotubes. The activation energy of β relaxation increases with carbon nanotube concentration. The percolation threshold is lower in composites with both thinner and oxidized carbon nanotubes. The established influence of both the MWCNT mean outer diameter and their oxidation on the broadband dielectric characteristics can be exploited for the production of effective low-cost electromagnetic and/or antistatic coatings working at different temperatures.