By Josh Perry, Editor
A research team from the Korea Advanced Institute of Science and Technology (KAIST) in Daejeon, South Korea used computer simulations to determine how the alignment between carbon nanotubes and polymers can produce next-generation carbon fiber materials.
Professor Yong-Hoon Kim and Ph.D. candidate Juho Lee. (KAIST)
According to a report from KAIST, adding carbon nanotubes (CNT) has been proposed to enhance the material’s orientation and crystallization, which had been a roadblock to improving carbon fiber properties. But, to make carbon nanotubes more effective, researchers needed to better understand the interface between the nanotubes and the polymer.
Researchers used density functional theory (DFT) calculations and force-fields molecular dynamics (MD) simulations to reveal the atomistic characteristics of the CNT-polymer interfaces. To perform the study, researchers used polyacrylonitrile (PAN)-CNT hybrid structures because PAN is the most common polymer precursor.
“Based on their DFT calculations, the team showed that the lying-down PAN configurations give a larger PAN-CNT binding energy than their standing-up counterparts,” the article explained. “Moreover, maximizing the lying-down PAN configuration was shown to allow linear alignments of PANs on CNT, enabling the desirable ordered long-range PAN-PAN packing.”
In addition, researchers saw that CNT curvature was also an issue, with the largest binding energy taking place in areas of zero-curvature. They also showed that graphene nanoribbons could be used to enhance PAN.
The research was recently published in Advanced Functional Materials. The abstract stated:
“While one of the most promising applications of carbon nanotubes (CNTs) is to enhance polymer orientation and crystallization to achieve advanced carbon fibers, the successful realization of this goal has been hindered by the insufficient atomistic understanding of polymer–CNT interfaces.
“Herein, polyacrylonitrile (PAN)?CNT hybrid structures are theoretically studied as a representative example of polymer–CNT composites. Based on density functional theory calculations, it is first found that the relative orientation of polar PAN nitrile groups with respect to the CNT surface is the key factor that determines the PAN–CNT interface energetics and the lying?down PAN configurations are much more preferable than their standing?up counterparts.
“The CNT curvature is identified as another important factor, giving the largest binding energy in the zero?curvature graphene limit. Charge transfer analysis explains the unique tendency of linear PAN alignments on the CNT surface and the possibility of ordered PAN–PAN assembly.
“Next, performing large?scale molecular dynamics simulations, it is shown that the desirable linear PAN–CNT alignment can be achieved even for relatively large initial misorientations and further demonstrate that graphene nanoribbons are a promising carbon nano?reinforcement candidate.
“The microscopic understanding accumulated in this study will provide design guidelines for the development of next?generation carbon nanofibers.”