TAILORING THE INTERFACE IN A HIERARCHICAL COMPOSITE BASED ON CARBON NANOTUBE FIBERS

An unconventional multi-scale, i.e. nano-micro-macro, hierarchical composite was designed by using the newly emerged carbon nanotube fibers (CNTFs). The CNTFs were densified with different solvents, i.e. ethylene glycol or nitric acid in this work in order to control the density of the CNTFs and to modify the surface of the fiber. Results showed that the treatment affect the penetration of the matrices and the interface between the CNTFs and the matrices. A continuously monitored single fiber fragmentation test was conducted to evaluate the interfacial shear strength. The results show strong effects of the solvents on the structure and chemistry of the CNTFs, and consequently on the interface of the hierarchical composites. Electron microscopy images provide a visual proof for differences at the matrix-CNTF interfaces, due to the treatments. A modified Cottrell-Kelly-Tyson model was applied to account for the wavy cross-sectional geometry of the CNTF and the effect of matrix penetration.

SEM images of CNTF(EG) (a) and CNTF(HNO₃) (b). (c) is the Birefringence pattern of the CNTF fragments under an optical microscope equipped with polarized light. Arrows indicate the breaks of the fiber under tension. The scale bars are 3 microns in (a) and (b), and 100 microns in (c).