Alignment of multiwalled carbon nanotubes in bulk epoxy composites via electric field

We demonstrate the alignment of multiwalled carbon nanotubes in bulk epoxy matrices by application of external electric field. The composites were prepared by a macro-layer-by-layer method; UV light was used to rapidly polymerize the epoxy and preserve the aligned nanotube network. The nanotube alignment generated strong anisotropy in the composite's properties. The composite's storage modulus was increased by similar to 50%, and the electrical conductivity was improved by four orders of magnitude in the direction of nanotube alignment. Compared to pristine nanotubes, amine functionalized nanotubes showed enhanced storage modulus but reduced electrical conductivty. The enhanced modulus for amine functionalized nanotubes is an artifact of their enhanced compatibility with the epoxy, while their reduced conductivity may result from the shortening of the nanotube length during functionalization. In addition to the rapid alignment of nanotubes parallel to the field direction, we also report a tendency for lateral agglomeration (perpendicular to the field) of the aligned nanotubes over time. Such a coarsening effect can be mitigated by minimizing the polymerization (or cure) time of the epoxy.