Interphase Development in Polyacrylonitrile/SWNT Nanocomposite and Its Effect on Cyclization and Carbonization for Tuning Carbon Structures

In this study, the self-stiffening behavior of polyacrylonitrile (PAN)/carbon nanotube (CNT) nanocomposites is used to develop the interphase structure. Instead of multi-walled carbon nanotubes (MWNTs), single-walled carbon nanotubes (SWNTs) were used, since they provide much more interfacial area with PAN matrix. The effects of SWNT content (0–1.5 wt %) and temperature on the structural development of PAN/SWNT nanocomposites during dynamic straining were compared for processing optimization. Using this unique dynamic straining method, we were able to tune the structures, especially the interphase of PAN/SWNT nanocomposites. The degree of crystallinity of nanocomposite could be improved from 54.3 to 58.5% after dynamic straining for 12 h, and the activation of the PAN glass transition increased from 434 to 1192 kJ/mol. The thermal behaviors of PAN and PAN/SWNT films with various degrees of crystallinity were compared by differential scanning calorimeter and thermal gravimetric analysis. The relationships among the structural parameters of a PAN film, its cyclization reaction, and carbonized structures were proposed. A higher degree of crystallinity of PAN would benefit a greater completion of cyclization reaction and lead to a higher carbon yield. Additionally, the high-resolution transmission electron microscope images of the carbonized PAN/SWNT nanocomposites commonly show the formation of graphitic structures, whereas the carbonized PAN films only contained amorphous carbon structures. Our findings not only deepen the understanding of how the physical structures of PAN affect its cyclization and carbonized structures but also provide a new way for making carbon materials with possibly much-improved graphitic structure, mechanical performance, and thermal/electrical conductivity.