AC-impedance response of multi-walled carbon nanotube/cement composites

AC-impedance spectroscopy (AC-IS) was combined with time-domain reflectometry (TDR) to investigate the impedance response of fiber-reinforced cement (FRC) composites with multi-walled carbon nanotubes (MWCNTs). In Nyquist plots (-imaginary impedance vs. +real impedance) three impedance arcs/features were observed, similar to Nyquist plots for macrofiber and microfiber FRCs. The intersection of the electrode arc and the intermediate frequency feature (R-DC(FRC)) corresponds to the DC resistance of the composite. The intersection of the two bulk features (R-cusp) corresponds to the AC resistance of the composite. Reductions in (R-DC(FRC)) from the matrix resistance are indicative of a nanotube percolating network. Reductions in R-cusp from the matrix resistance are indicative of a discontinuous fiber-fiber path. Both shifts increased with fiber loading. AGIS measurements are therefore able to discriminate percolation vs. discontinuous fiber effects in CNT-FRCs, with the potential for characterizing dispersion issues (e.g., clumping/aggregation) in nanocomposites. (C) 2006 Elsevier Ltd. All rights reserved.