Figure 3. Thermogravimetric analysis and derivative thermogravimetric
analysis of the multi-walled carbon nanotubes for the preparation of
epoxy matrix composite materials.
The Raman spectra of the multi-walled carbon nanotubes are illustrated
in Figure 4 for the preparation of epoxy matrix composite materials.
Although Raman spectroscopy is a powerful analytical method for
molecular analysis, Raman spectra are often plagued with intense
fluorescence backgrounds resulting from impurities or from the
population of a sample's excited states. Algorithm-based methods attempt
to mathematically estimate a baseline and then subtract the estimated
baseline from the Raman spectrum to give a fluorescence free spectrum.
Algorithm-based methods suffer from the requirement that they cannot be
applied to all types of fluorescence without either significant
degradation in performance or significant user intervention to adjust
sensitive algorithm parameters. One reason for this disadvantage is the
varied nature of fluorescence backgrounds. Another reason is due to the
complexity of the fitting algorithms. A carbon nanotube has a shape in
which flat graphite is wound in a cylindrical shape. The carbon nanotube
may be a carbon nanotube into which a single-walled carbon nanotube is
incorporated. Single-walled carbon nanotubes have a structure in which
one layer of graphite is wound. A multi-walled carbon nanotube has a
structure in which two or three or more layers of graphite are wound.
Furthermore, a side wall of the carbon nanotube may not have a graphite
structure. For example, a carbon nanotube having a side wall having an
amorphous structure can be used as the carbon nanotube. The G to D ratio
is 1.5 to 5.0, wherein G represents the maximum peak intensity in the
range from 1560 to 1600 per centimeter and D represents the maximum peak
intensity in the range from 1310 to 1350 Per centimeter in the Raman
spectra. There are various laser wavelengths used in Raman spectroscopy,
but in the present specification, 532 nm and 632 nm are used. A Raman
shift observed near 1590 per centimeter in the Raman spectrum is called
a G band derived from graphite, and a Raman shift observed near 1350 per
centimeter is called a D band derived from a defect of amorphous carbon
or graphite. As a G to D ratio of the carbon nanotube becomes higher, a
degree of graphitization becomes higher.