Dielectric properties of polymethacrylate-grafted carbon nanotube composites

Abstract

The dielectric properties of a series of multi-walled carbon nanotubes on which poly(cyclohexyl methacrylate)s were densely grafted (PCHMA-CNTs) were systematically characterized over the broad frequency range of 10⁻²–10⁸ Hz. PCHMA-CNT was used as an ideal polymer/CNT nanocomposite system in which the CNT is homogeneously dispersed and the polymer/CNT interface is strong. When the volume fraction of the CNT Φ_CNT < 0.1 PCHMA-CNT exhibited a relatively high dielectric constant ε′_r and a quite low dielectric loss factor ε′′_r, while when Φ_CNT > 0.1 a very large ε′_r was observed at low frequencies. The Cole–Cole relaxation model was applied to the impedance spectra of PCHMA-CNT in order to investigate the correlation between the tunneling conduction and the very large ε′_r. Also, from thus-obtained relaxation frequencies, the inter-nanotube distance in the PCHMA-CNT system was estimated. As a result, a new mechanism was proposed for the very large ε′_r: the locally enhanced electric field by the tunneling conduction results in the very large ε′_r at the low frequencies along with the increase in ε′′_r. Furthermore, the CNT was demonstrated to be five times more effective than barium titanate (BT) for the enhancement in ε′_r of polymer materials because of the higher electric field enhancement effect of the CNT than that of the BT.