Dielectric properties of multiwall carbon nanotube-epoxy composites

Resin and functionalized multiwall carbon nanotubes (fMWCNT) were used to obtain composites, cured at room temperature (RT). Dielectric measurements show changes of permittivity and losses in cooling-heating cycle with non-reproducible values above 50 degrees C. Interplay of segments with increased mobility due to increasing resin temperature, the differences between thermal expansion coefficients between resin and fMWCNT, spatial rearrangements in samples and post curing effects could explain the evolution of dielectric parameters versus temperature. Permittivity and losses show strong frequency dependence associated with reducing contributions of different polarization mechanisms at increasing frequencies. Permittivity, losses and electrical conductivity of the samples reveal a tremendous increase with nanotubes concentration at the percolation threshold. Percolation and tunneling mechanisms at RT and thermally activated mechanisms, which dominates the electrical conduction at high temperatures, can explain the temperature dependence of samples' conductivity. Electrical measurements also showed non-reproducible values at heating and cooling beyond 55 degrees C.