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Reinforcing composite materials with carbon nanotubes (CNTs) has the potential to improve mechanical and/or multifunctional properties due to their nano-size. Research has been done on using CNTs to reinforce the interlaminar strength of carbon fiber reinforced composites (CFRPs), but most of the previous work is about randomly oriented carbon nanotubes. Currently, one of the main challenges regarding CNT integration into polymers is mitigating their agglomeration and controlling their dispersion in the polymer matrix. By aligning CNTs with an external field, more tailored structure control can be achieved, and a better understanding of how CNT agglomeration and dispersion relate to external field application and CNT concentration is needed. In this work, we studied the effects of magnetic field magnitude, CNT concentration, and matrix viscosity on CNT agglomeration and morphology. We measured the fracture toughness reinforcement of epoxy-CNT nanocomposites at various CNT concentrations (0.1 vol.% and 0.5 vol.%), magnetic field magnitudes (no field, 180 G, and 300 G), and matrix viscosities (older epoxy-hardener system with higher viscosity and newer epoxy-hardener system with lower viscosity). Our results demonstrated that aligning CNTs with a magnetic field can lead to extra reinforcement when compared to using randomly oriented CNTs if the field magnitude, CNT concentration, and matrix viscosity are selected accordingly. The maximum fracture toughness reinforcement achieved with the higher viscosity epoxy-hardener system (~72%) was with 0.5 vol.% of CNTs with a 180 G field, whereas the maximum reinforcement with the lower viscosity epoxy-hardener system (~62%) was observed for the samples fabricated with 0.1 vol.% of randomly oriented CNTs. COMSOL simulations were also conducted to understand the behavior of CNT agglomeration and alignment at different field magnitudes and CNT concentrations, and were compared with the experimental results. To maximize CNT reinforcement, more work needs to be conducted to address the challenge of CNT agglomeration and dispersion control in a polymer matrix, such as a more in-depth study of how different field magnitudes affect fracture toughness improvement and new methods to improve CNT dispersion. 

Organization of carbon nanotubes (CNTs) within epoxy matrices can be effectively achieved using magnetic field application. In our previous experimental work, multi-walled CNTs were magnetized, diazotized, and magnetically aligned to form aligned CNT-epoxy composites. While effective toughness improvement was experimentally observed with small CNT addition, more understanding about magnetic assembly of CNTs is desired, to effectively complete CNT assembly before the epoxy cures and also to avoid re-agglomeration of CNTs. In this work, assembly behaviors of ellipsoid particles, that simulate CNT bundles, in a fluid domain, that simulates the epoxy matrix, under the static magnetic field are being studied. Higher ellipsoid aspect ratio was observed to be effective to decrease the magnetic assembly time, while some ellipsoid lower aspect ratio and larger original ellipsoid separate distance combination prevented their magnetic assembly. When assembly is achieved, the assembly time was observed to be much smaller (<0.1 second) than the currently dedicated assembly time in our experiments (~10s of minutes). Further studies with more ellipsoids, varying ellipsoid positions, and increasing magnetic field strength are planned in future.