Electrical and thermal properties of epoxy matrix composite materials reinforced with multi-walled carbon nanotubes under different weight fraction conditions

The present study is focused primarily upon the electrical and thermal properties of epoxy matrix composite materials reinforced with multi-walled carbon nanotubes under different weight fraction conditions. Stable suspensions of carbon nanotubes are achieved in water with the use of surfactants, and non-covalent and covalent attachment of polymers. Scanning electron microscopy characterization is performed and electrical resistance is measured. Mechanical properties are studied and the loading rate is continuously adjusted to keep a constant representative strain rate. The Oliver-Pharr method is used to analyze partial load-unload data in order to calculate the indentation elastic modulus as a function of the indenter penetration. The present study aims to provide an improved method for the preparation of epoxy matrix composite materials reinforced with multi-walled carbon nanotubes with reduced volume resistivity and enhanced thermal conductivity. Particular emphasis is placed upon the effect of carbon nanotube weight fraction on the volume resistivity and thermal conductivity of the epoxy matrix composite materials reinforced with multi-walled carbon nanotubes. The results indicate that single-walled carbon nanotube structures can have smaller effective pore size than multi-walled carbon nanotube structures. Single-walled carbon nanotubes are harder to disperse and more difficult to functionalize than multi-walled carbon nanotubes. Heat resistance of carbon nanotubes varies depending on the diameter of carbon nanotubes and the quality of a graphene sheet constituting the wall of carbon nanotubes. As a G to D ratio of the carbon nanotube becomes higher, a degree of graphitization becomes higher. The single-walled carbon nanotube-reinforced fracture surfaces express substantial increases in the micron-level surface roughness. The multi-walled carbon nanotubes interact with the crack path and result in crack deflection and a more torturous fracture path. The percolation threshold for conductive particles embedded in an insulating polymer matrix is sensitive to the structure of the reinforcement, and the decrease in electrical resistivity with an increase in reinforcement content is attributed to the probability of reinforcement contact. Unlike electrical conductivity, where a sharp percolation threshold is achieved, the increase in thermal conductivity with increasing carbon nanotube concentration is nearly linear. Keywords: Electrical properties; Thermal properties; Carbon nanotubes; Electrical conductivity; Thermal conductivity; Thermogravimetric analysis