Figure 4. Raman spectra of the multi-walled carbon nanotubes for the preparation of epoxy matrix composite materials.
The scanning electron micrographs of the epoxy matrix composite materials are illustrated in Figure 5 which are reinforced with single-walled carbon nanotubes. The fracture surface is relatively smooth and absent of any structural features. The single-walled carbon nanotube-reinforced fracture surfaces express substantial increases in the micron-level surface roughness. This increase in surface roughness is the likely reason that the nanocomposites express enhanced fracture toughness. In the resultant polymer carbon nanotube composites, the carbon nanotubes are an integral part of polymer chains rather than separate fillers within a polymer matrix. Polymer-carbon nanotube composites where the carbon nanotube is chemically associated with the polymer has the advantage that load can be transferred to the nanotubes which provides enhanced mechanical properties to the composite and also helps prevent separation between the polymer surface and the carbon nanotubes. The thermal and electrical properties of the carbon nanotubes can also be exploited in this way. The at least one oxygen moiety of the carbon nanotubes are reacted with a suitable molecule to form a carbon nanotube macromer before being reacted with the at least one monomer to attach polymer chains to the sidewalls of the carbon nanotubes. The reaction between the carbon nanotube-molecule complex and the at least one monomer may be activated or initiated through the application of energy in the form of heat or by the presence of a suitable chemical initiator. However, individual carbon nanotubes tend to agglomerate, which tends to complicate subsequent processing. For example, agglomeration of individual carbon nanotubes tends to clog nozzles used in fused deposition modeling. More specifically, fused deposition modeling works by laying down material in layers from a polymer filament to form the shape of the article having final or near-final dimensions. However, as individual carbon nanotubes tend to agglomerate, processing becomes complicated due to clogging of a nozzle used to lay down the layers of a polymer incorporated with individual carbon nanotubes. Also, individual carbon nanotubes may become airborne, raising concerns with handling of the carbon nanotubes. The dimensions of the carbon nanotube sheetlets are not limited and may depend upon the application of the carbon nanotube enhanced polymer. If the dimensions of the carbon nanotube sheetlets are too small, then concerns with handling of the carbon nanotubes may be raised. A width of the carbon nanotube sheetlets is not limited and may depend upon the application of the carbon nanotube enhanced polymer.