Uniform and scalable carbon nanotube growth on carbon fibers: Insights from experimental dynamic snapshots and computational fluid dynamics

Carbon nanotube (CNT) grafted carbon fibers (CFs) are promising for multifunctional composites (CFRPs) but remain limited by scalability, non-uniform growth, and degradation of fiber tensile strength. This paper reports a continuous spool-to-spool chemical vapor deposition (CVD) process that achieves uniform CNT growth throughout 12k CF tows while preserving fiber tensile properties. The uniformity of CNT coverage, over meters of length and across thousands of fibers, was objectively established via a multi-length scale characterization protocol, combining machine learning-based SEM classification with macroscopic measurements of BET-based specific surface area (SSA) and gravimetric CNT content. Microscopic and macroscopic measurements are independently self-consistent. To understand and optimize CNT growth, a new dynamic snapshot method was developed and combined with steady-state computational fluid dynamics (CFD) modelling to resolve the spatial evolution of catalyst activation, nucleation, and CNT growth kinetics as a function of reactor temperature and species concentrations. These insights informed targeted modifications to gas flow and temperature conditions, enabling reproducible CNT growth at 550 °C. Under optimized CVD conditions, the CFs were grafted with a CNT corona of 850 nm in length, corresponding to a loading of 2.9 wt% on the fibers, which led to a ten-fold increase in SSA (5.35 m2 g−1). The process was shown to be stable for extended lengths (>50 m) and reproducible across multiple runs, establishing a scalable route for integrating CNT-grafted CFs into conventional manufacturing. This experimental-computational framework provides a rational approach toward high-performance multifunctional, hierarchical CFRPs.