Carbon nanotubes are excellent candidates for the development of nano-reinforced polymer composite materials. However, assurance of homogeneous dispersion, interfacial compatibility between the carbon nanotube and the polymer, and exfoliation of the aggregates of carbon nanotubes, are required for the successful integration of carbon nanotubes into nanocomposites. The present study is focused primarily upon the electrical and mechanical properties of catalytically-grown multi-walled carbon nanotube-reinforced epoxy composite materials. Particular emphasis is placed upon the effect of carbon loading on the electrical conductivity and the influence of temperature on the loss factor and modulus for the composite materials. The results indicate that the electrical properties of the composite would not be changed from those of the bulk polymer until the average distance between the carbon nanotubes is reduced such that either electron tunneling through the polymer or physical contacts may be formed. Among the challenges introduced in the fabrication of carbon nanotube-filled polymer composites is the necessity to creatively control and make use of surface interactions between carbon nanotubes and polymeric chains in order to obtain an adequate dispersion throughout the matrix without destroying the integrity of the carbon nanotubes. Frequency domain material properties are therefore limited to applications where strains are small and stress is approximately linear with strain and the strain rate. Frequency domain material properties become irrelevant if the material exhibits nonlinear elastic behavior or is subjected to large strains. Depending on the type of polymers in the matrix, above a certain temperature limit, degradation starts or cross-linking starts. The deformed elastic body possess an amount of potential energy equal to the initial amount of potential energy minus the amount of energy irreversibly dissipated. The modulus and loss factor variables of a damping material are highly dependent upon the temperature of the damping material and the vibration frequency. Because of their viscoelastic nature, the stress and strain in viscoelastic materials are not in phase, and, in fact, exhibit hysteresis. The resonant frequency is related to the modulus of the catalytically-grown multi-walled carbon nanotube-reinforced epoxy composite.

Keywords: Composite materials; Electrical properties; Mechanical properties; Carbon nanotubes; Electrical conductivity; Loss modulus