Relationship between the carbon nanotube dispersion state, electrochemical impedance and capacitance and mechanical properties of percolative nanoreinforced OPC mortars

Abstract

The homogeneous dispersion of carbon nanotubes, (CNTs), in a cementitious matrix is a crucial procedure that affects both mechanical properties and electrical conductivity of the nanocomposite. Electrochemical Impedance Spectroscopy, (EIS), can be very useful in studying and characterizing the impact of the CNT content in nanoreinforced cementitious materials in a quantitative way. In this study, measurements of the resistance, reactance and capacitance reveal the nature of circuit elements formed by the nanotube network in cement mortars reinforced with various amounts of carbon nanotubes and provide insight of the nanotubes’ dispersion state. Resistivity results show that percolation threshold was reached between CNT weight fractions of 0.1% and 0.15 wt%. Below percolation, a consistency between resistive and capacitive phases exists, i.e., resistivity, reactance and capacitance were found to decrease as the nanotube content increases. After the continuous conductive network was formed, and percolative behavior was achieved, resistivity values show a little dependence on the CNT content. However, the presence of CNT entanglements was found to contribute to an amplified energy storage ability, as both the imaginary part of impedance (reactance) and capacitance were increased. A correlation between capacitance, flexural strength and modulus of elasticity was observed for the first time. Capacitance values provide valuable information on the energy storage ability of the material and how the actual CNT dispersion state affects the mechanical properties of percolative nanoreinforced cementitious materials. Finally, a general micromechanics model, modified by taking into account the conductive mechanisms below and above percolation threshold, was successfully implemented. The theoretically determined values of the overall electrical conductivity are in good agreement with the experimental results.