Microwave Swelling and Exfoliation of Continuous Carbon Nanotube Networks for Scalable Manufacturing of Nanocomposites

Rapid heating of carbon nanotube (CNT) materials via microwave-induced heating is known to enable efficient chemical functionalization and accelerated curing of composites. Both liquid-phase and solvent-free techniques rely on the large dielectric loss of CNT materials, which causes them to absorb incident microwave energy. However, despite the prevalence of liquid-phase techniques in the processing of continuous CNT networks (e.g., CNT yarns and tapes), to our knowledge a detailed exploration of microwave heating of continuous CNT networks imbibed with liquid is not present in literatured. Here, we study liquid-phase microwave heating of CNT networks using commercially produced nanoporous CNT yarns as a model system. We observe that rapid heating of immersed CNT networks causes macroscopic swelling of CNT yarns and even exfoliation of CNT bundles, increasing their porosity and surface area while preserving their continuity and crystallinity. Through selection of appropriate solvents and heating rates, this swelling is found to be controllable. Swelling isminimized via low heating rates (i.e., 1–3 °C min–1), which allow for thermal equilibration, and maximized using microwave-transparent, low-loss solvents with low boiling points. Accordingly, we believe that the microwave-superheated liquid environment is particularly promising for manufacturing advanced CNT materials, which can benefit from this physical modification. By exploiting this intrinsic behavior in the presence of various reactants, liquid-phase microwave processing may enable faster and more effective functionalization or decoration of CNT yarns or in situ synthesis of polymer nanocomposites.