Processing of hybrid advanced composites utilizing capillarity-driven wetting of aligned carbon nanotubes

Processing nanostructures such as carbon nanotubes (CNTs) into polymers to create multifunctional hybrid advanced composites has significant challenges, such as agglomeration, viscosity, and the relative inability to align or otherwise organize the nanostructures. Many of these issues may be overcome by utilizing as-grown aligned CNTs. Several hybrid advanced composite architectures have been developed that are comprised of standard advanced fibers and polymers (e.g., graphite/epoxy) plus aligned CNTs distributed inside the polymer. CNT alignment is advantageous from a property-tailoring perspective, but is also crucial for polymer wetting to achieve a well-consolidated composite. The mechanism of capillarity-driven wetting of the aligned CNTs is explored analytically and used to motivate manufacturing of several composite systems: hand layup of woven fabric with CNTs grown on the fibers in the fabric, aligned CNT reinforcement of prepreg interfaces, and resin infusion with aligned CNT reinforcement of the ply interface. Characterization of these laminates after fabrication by optical and scanning-electron microscopy reveals effective wetting of the aligned CNTs. A new experimental setup for extracting the effective contact angle of the liquid-CNT interface in such a porous aligned-nanostructure morphology is described and used to quantify key capillarity parameters for wetting of aligned-CNT forests. Ongoing work is seeking to further quantify wetting rates in CNT forests for various polymers and explore the efficacy of aligned vs. tangled CNT wetting.