Multilevel composite using carbon nanotube fibers (CNTF)

Multilevel hierarchical structures built up from nanoscale to macroscale are common in nature, but their potential has not been achieved by man-made composites. The presented multilevel structure consists of carbon nanotube fibers (CNTFs) embedded in epoxy matrix. This structure exploits the supreme mechanical properties of individual CNTs together with the manageability of the microscale CNTFs, and has the potential to overcome the implementation difficulties associated with nanocomposites. Using different chemical treatments (ethylene glycol or nitric acid solvents), the CNTFs are densified and the amount of epoxy penetration inside the CNTFs is controlled, creating an interphase between the single CNTs. The strength and adhesion properties of individual CNTFs in epoxy are measured by continuously monitored fragmentation tests and characterized by electron microscopy. A modified Cottrell-Kelly-Tyson model is applied to account for the CNTF unique cross-sectional geometry, comprising millions of individual multiwalled CNTs, and for the effect of matrix penetration. The composite strength and toughness are found to be strongly dependent on and improved by the extent of penetration, suggesting that the composite mechanical properties would be tunable by controlling the interphase. The presented integrative analysis shows that CNTF based composites are an excellent potential choice for strong and tough structures, as well as for bio-engineering.