Since their first observation in 1991 by Iijima, carbon nanotubes have been the focus of significant research. In particular, single-walled carbon nanotubes (SWNTs), a type of fullerene structure, received considerable notice because of their exceptional stiffness and strength. For example, their fracture strains are estimated to be 10%-30%, a factor of 10-100 times better than the carbon fiber IM7, a fiber commonly employed in military and aerospace applications. Even though the true properties of nanotube-reinforced nanocomposites have not been tested or demonstrated, the composite community considers their extremely high specific modules and strength, coupled with a tensile strength higher than conventional carbon fibers, qualify carbon nanotubes as the ideal reinforcement for polymer composite materials.
Current nanotube-reinforced nanocomposites were usually prepared by solution mixing and casting or by melt dispersion and injection techniques. Although better mechanical properties of the nanocomposites have been reported, these techniques do not yield expected properties due to non-uniform SWNT dispersion, lack of SWNT orientation, and limitation of SWNT volume content. Consequently, the resultant materials fail to live up to the quality anticipated.
In this study, a new nanocomposite processing method based on SWNT network preforming and resin infiltration techniques is investigated. Well-dispersed and controlled nanostructure composites with high SWNT content were fabricated and characterized. Preformed SWNT networks or nanotube bucky papers (NBPs), which are thin sheets (films) formed with well-controlled dispersion and porous network of SWNTs, were prepared by multiple-step dispersion and filtration processes of nanotube suspension. The NBPs were then wetted with Epon 862 epoxy resin to make the nanocomposite material. The complex interactions between the resin molecules and SWNTs within the NBPs nanoscale porous structures during the composite processing were studied by molecular dynamics (MD) simulation analysis. In this research, preformed nanotube networks with desired dispersion and porous structure in the NBPs were produced and used for fabricating composites. The nanostructure and the wetting between SWNTs and the epoxy resin were observed with AFM and SEM. The NBPs pore sizes varied between 10 nm to 200 nm depending on the processing parameters and the uniformity of the dispersion of SWNTs. The nanocomposites with high SWNT content (>20v%) and well-controlled nanostructure were fabricated. The experimental results indicate that satisfactory resin infiltration and wetting were achieved. The MD simulation shows that resin molecules have both the tendency to spread on the SWNT surface and the aggregation during processing.
This study shows that the new nanocomposite processing technique with prefomed NBP and resin infiltration is an effective way to prepare nanotube-reinforced nanocomposites with desired nanostructure and high nanotube content. It was also shown that the complex interactions between nanotubes and polymer molecules at the nanoscale during the composite processing can be analyzed using the MD simulation technique.
Industrial Engineering, Florida A&M University-Florida State University College of Engineering
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