  In building up composite structures using carbon nanotube (CNT) fibers, the
fiber-to-matrix interfacial shear strength (IFSS) is one of the most important
issues. Originating from the assembly characteristics of CNT fiber, the IFSS
strongly depends on the fiber's twisting level and densification level.
Furthermore, there are rich ways to modify the fiber surface and thus enhance
the IFSS, including the physical and chemical modification on fiber surface,
the infiltration of matrix resin into CNT fiber, and the introduction of silane
coupling agent. A new feature differing from carbon fibers is that all these
treatments either change the fiber's surface structure or form a
several-hundreds-nm-thick interphase inside rather than around the fiber. These
"generalized" treatments obviously extend the common concept of surface sizing
and can be used for various forms of CNT assembly structures.
