Multi-step mechanism of carbonization in templated polyacrylonitrile derived fibers: ReaxFF model uncovers origins of graphite alignment

Understanding the atomistic mechanisms of carbon structure formation during templated multi-step carbonization is very important for further optimization of carbon fiber mechanical properties. Here with use of reactive force field molecular dynamics we have elucidated the mechanism driving double-walled carbon nanotube- and graphite nanoparticle-based in situ templating of polyacrylonitrile derived fibers. Depending on carbonization temperature, the mechanism involves either physisorption (physical templating) or chemisorption (chemical templating) of the fiber medium to the template surface. In either case, strong interaction between template and medium leads to the production of aligned structures that are more robust for nanotubes than graphite. We provide a unique analysis of atomistic simulations that enables quantitative comparison of templating results with the relevant electron diffraction data.