Cross-links in carbon nanotube assembly introduced by using polyacrylonitrile as precursor

Individual carbon nanotube (CNT) exhibits extraordinary mechanics. However, the properties of the macroscopic CNT-based structure, such as CNT fibers and films, are far lower than that of individual CNT. One of the main reasons is the weak interaction between tubes and bundles in the CNT assemblies. It is understood that the cross-links in CNT assembly play a key role to improve the performance of CNT-based structure. Different approaches have been taken to create CNT joints. Most of these approaches focus on connecting CNTs by generating new covalent bonding between tubes. In this work, we intend to reinforce the CNT network by locking the contacted CNTs. Polyacrylonitrile (PAN) was used as precursor because PAN can form graphitic structures after carbonization. The freestanding superthin CNT sheet and CNT yarn were used to evaluate the effects of the PAN precursor to form cross-links between CNTs. The tensile strength of CNT yarn is improved when the yarn is partially infiltrated with PAN and consequently carbonated. High-resolution transmission electron microscopy observation of the sheets shows that graphite structures are formed and cross-link CNTs in CNT assembly.