A New, General Strategy for Fabricating Highly Concentrated and Viscoplastic Suspensions Based on a Structural...

We report a general strategy to fabricate highly concentrated, viscoplastic and stable suspensions by designing the particle surface structure to control the interparticle attractive forces. Unlike conventional methods, where the choice of solvent is critical in balancing interparticle interactions, suspensions showing excellent stability and viscoplastic properties were made using various solvents. We demonstrated this approach using highly sparse agglomerates of carbon nanotubes (CNTs) as the particles. Our results revealed that the essential feature of the CNT agglomerate to fabricate these suspensions was high porosity with a spacing size much smaller than the overall size, which was only possible using long single-walled carbon nanotubes (SWNTs). In this way, the agglomerate surface was characterized by fine network of CNT bundles. These suspensions exhibited solid-like behavior at rest (characterized by a high yield stress of c.a. 100 Pa) and a liquid-like behavior when subjected to a stress (characterized by a significant drop of an apparent viscosity to 1 Pa·s at a shear rate of 1000 s^-1). Furthermore, in contrast to conventionally fabricated suspensions, these "CNT pastes" exhibited exceptional stability at rest, under flow, and at extremely high concentrations during the drying process, with only a weakly observable dependence on solvent type. As a result, highly uniform micrometer-thick SWNT films were successfully fabricated by dried blade-coated films of these pastes. Finally, we developed a simple, semiempirical model and clarified the importance of the CNT agglomerate microstructure (the ratio of spacing size/particle size and porosity) on tailoring the cohesive forces between particles to fabricate stable viscoplastic suspensions.