Thermoforming nanoparticle aggregates via interfacial ionic self-diffusion

Dense aggregates of nanoparticles often exhibit excellent physical properties but have no thermoplasticity. Their formation processes are thus limited to drying of dilute nanoparticle dispersions, resulting in thin flat sheets or slender filaments. This limitation hinders the application of nanoparticle aggregates. In this study, we developed a thermoforming strategy for nanoparticle aggregates using wood-derived cellulose nanofibers (CNFs). CNF aggregates with thermoplasticity were formed by introducing anionic functional groups onto the CNF surfaces, followed by pairing the anions with highly dissociable ionic liquid (IL) counterions. Heat-induced self-diffusion of the IL counterions at the interfaces between CNFs within an aggregate allowed thermoforming of CNF aggregates, such as three-dimensional molding, position-selective sealing, and multilayer lamination of sheets. This thermoforming strategy was also applicable to two-dimensional carbon nanoparticle (graphene oxide) systems.