Joint Theoretical and Experimental Study of Stress Graphitization in Aligned Carbon Nanotube/Carbon Matrix Composites

Stress graphitization is a uniquephenomenon at the carbon nanotube(CNT)-matrix interfaces in CNT/carbon matrix (CNT/C) composites.A lack of fundamental atomistic understanding of its evolution mechanismsand a gap between the theoretical and experimental research have hinderedthe pursuit of utilizing this phenomenon for producing ultrahigh-performanceCNT/C composites. Here, we performed reactive molecular dynamics simulationsalong with an experimental study to explore stress graphitizationmechanisms of a CNT/polyacrylonitrile (PAN)-based carbon matrix composite.Different CNT contents in the composite were considered, while thenanotube alignment was controlled in one direction in the simulations.We observe that the system with a higher CNT content exhibits higherlocalized stress concentration in the periphery of CNTs, causing alignmentof the nitrile groups in the PAN matrix along the CNTs, which subsequentlyresults in preferential dehydrogenation and clustering of carbon ringsand eventually graphitization of the PAN matrix when carbonized at1500 K. These simulation results have been validated by experimentallyproduced CNT/PAN-based carbon matrix composite films, with transmissionelectron microscopy images showing the formation of additional graphiticlayers converted by the PAN matrix around CNTs, where 82 and 144%improvements of the tensile strength and Young's modulus areachieved, respectively. The presented atomistic details of stressgraphitization can provide guidance for further optimizing CNT-matrixinterfaces in a more predictive and controllable way for the developmentof novel CNT/C composites with high performance.