Preliminary demonstration of energy-efficient fabrication of aligned CNT-polymer nanocomposites using magnetic fields

Preliminary fabrication of thermoset nanocomposites with aligned carbon nanotubes (CNTs) is demonstrated using magnetic fields in an energy-efficient and quick manner. Bulk application of high-performance polymer nanocomposites is currently limited because scalable manufacturing methods to deliver bulk samples with organized nanofillers are currently missing. In this work, active assembly using external magnetic fields is selected as a solution to provide the balanced benefits of bulk processing capacity and tailorable patterning capability. Magnetically-responsive multi-walled carbon nanotubes (∼35 nm diameter and ∼200 μm length) were fabricated with relatively simple post-growth processing: low-temperature oxygen plasma treatment for improved suspension and dispersion within matrices, and e-beam coating with thin ferromagnetic nickel (Ni) layers (∼40–100 nm) for larger magnetic susceptibility. Dispersion and properties of the plasma-treated and Ni-coated CNTs were evaluated visually using the settlement study and scanning electron microscopy, and quantitatively using Raman spectroscopy, X-ray photoelectron spectroscopy, and vibrating sample magnetometry. Assembly of Ni-coated CNTs was first demonstrated in deionized water, and then in a bisphenol-F based polymer resin (Epon 862). Magnetic assembly behaviors of these two-dimensional nanofillers were studied about the effect of their original dispersion, size, and matrix viscosity. The first sizable fabrication of CNT-thermoset nanocomposite (∼32 mm × ∼32 mm × ∼5 mm sample size) was attempted and demonstrated with the smaller magnetic field in the shorter time (∼400 G application for 40 min), than the previous attempt to assemble CNTs (∼10⁵ G for a few hours). Future work include homogenization of CNT patterns within the nanocomposites by improving the original CNT dispersion and suspension (ferromagnetic filling instead of coating, particle surface treatment, etc.), more complex CNT patterning using magnetic field parameter modulation, and structure-interface-property studies by polymer nanocomposite characterization, specially about transport properties.