Length-dependent broadband electric properties of PMMA composites filled with carbon nanotubes

Abstract

Broadband dielectric/electric properties of multiwalled carbon nanotubes (MWCNT) polymethylmetacrylate composites were studied in a wide temperature range (25–400 K). It was established that the percolation threshold is lower in composites with the shortest MWCNT, due to the better distribution of the MWCNT in the polymer matrix. The value of the dielectric permittivity and the electrical conductivity below the percolation threshold is also higher in composites with the shortest MWCNT. Below the percolation threshold the dielectric dispersion in composites is mainly related with the β relaxation in the polymer matrix. The length of the MWCNT and its concentration have also the huge influence on polymer matrix molecular dynamics, the relaxation time is shortest in composites with the higher MWCNT concentration and in composites with the shortest MWCNT. At low temperatures the conductivity of composites above the percolation threshold is governed by an electron tunneling between MWCNT clusters. At higher temperatures the electrical transport occurs also due to the finite electrical conductivity of the polymer matrix.