Carbon nanotubes on carbon fibers: Influence of growth conditions on fiber tensile properties

The interface between carbon fibers (CFs) and the resin matrix in traditional high performance composites is characterized by a large discontinuity in mechanical, electrical, and thermal properties which can cause inefficient energy transfer. Due to the exceptional properties of carbon nanotubes (CNTs), their growth at the surface of carbon fibers is a promising approach to controlling interfacial properties and achieving enhanced properties. However, the reactive conditions used to grow carbon nanotubes also have the potential to introduce defects that can degrade the tensile properties. In this study, high density multi-wall carbon nanotubes were grown directly on IM-7 and T650 carbon fiber using thermal chemical vapor deposition (CVD). The influence of CVD growth conditions on the single-fiber tensile properties and CNT morphology was investigated. The mechanical properties of sized fibers were shown to be sensitive to CVD growth conditions with significant decreases in properties at temperatures above 7000C. In contrast, the tensile properties of the unsized T650 fibers after growth of aligned CNTs at 750°C were similar to the initial untreated fiber. When the growth temperature was raised to 800°C and the flow rate of the reactive xylene/ferrocene mixture was increased, a nonaligned CNT morphology was obtained for the unsized T650 fiber. This demonstrated the capability to vary CNT morphology. However, the tensile properties of the fibers were degraded relative to those grown at 750°C. At a growth temperature of 700λC, no appreciable growth was obtained. In short, it is possible to vary the morphology of the CNTs grown on CF and to obtain CNT/CF assemblies with equivalent tensile properties to that of the initial fibers by varying CVD growth conditions and proper selection of the carbon fiber. Thus, growing CNT on the CF provides a viable means to tailor the thermal, electrical and mechanical interfacial properties of composites without necessarily sacrificing tensile properties.