Controlled Fabrication of Carbon Nanotube Microspheres from Emulsion Templates: Exploring the Dynamics of Solvent Loss and Nanoparticle Assembly

The use of emulsions as templates for nanomaterial assembly is a versatile method to create controlled microstructures. However, production rates are often low, particularly where the droplet phase solvent must be removed to achieve consolidation. Here, we study the emulsion templated fabrication of microparticles from multi-walled carbon nanotubes (CNTs). As an exemplar primary nanoparticle for microparticle assembly, CNTs present particular challenges due to their strong inter-particle interactions and limited dispersion in solvents. Nevertheless, small batches of CNT microparticles have demonstrated promising performances in energy storage, environmental remediation, and sensing due to their controlled structures. Improving CNT microparticle production through emulsion processing is therefore interesting to promote these real-world applications. In this work, we show that the slow rate of CNT microparticle formation from water-in-oil emulsions is due to spontaneous emulsification. We then test methanol-in-oil emulsions, which rapidly form fragile CNT capsules. Using mixtures of methanol and water, a faster rate of solvent loss can be balanced alongside nanoparticle assembly; CNT microparticle formation was up to twice as fast using 40% methanol compared to aqueous dispersions. In addition to facilitating faster CNT microparticle production, these findings offer more broadly applicable insights into the mechanisms of solvent transport in emulsions.