Assembly dependent interfacial property of carbon nanotube fibers with epoxy and its enhancement via generalized surface sizing

The fiber-to-matrix interfacial shear strength (IFSS) plays a key role in building up composite structures using carbon nanotube (CNT) fibers. 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 surface modification, the infiltration of matrix resin, and the introduction of silane coupling agent. As a new feature different from carbon fibers, these treatments either change the fiber's surface or form an interphase inside rather than around the fiber, and extend the common concept of surface sizing. The assembly structure of CNT fiber allows rich and different surface treatments to improve the interfacial shear strength (IFSS) as compared to carbon fibers. These treatments generalize the common concept of surface sizing by introducing an interphase inside rather than around the CNT fiber. The IFSS can be improved by more than 27%, from 47.7 to 60.6 MPa.