4. Conclusions
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. 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
major conclusions are summarized as follows:
- 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 wherein G and
D represent the maximum peak intensity, 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.