Intrinsic Geometric Conformation and the Phase and Nonlinear Flow Behavior of Carbon Nanotube Dispersions

The phase and flow behavior of carbon nanotube (CNT) dispersions is commonly described using parameters such as aspect ratio and persistence length, which do not explicitly account for permanent geometric waviness. Here, we compare three commercial CNTs with distinct intrinsic morphologies to examine how CNT conformation is associated with the mesoscale organization and nonlinear flow behavior of aqueous dispersions. Although all three would conventionally be classified as rigid rods based on their persistence lengths, two exhibited pronounced waviness whereas the third was relatively straight. Building on the rigid random coil (RRC) concept, the wavy CNTs were classified as RRC-CNTs and the straight CNT as a rigid rod (RR)-CNT. With increasing concentration, the RRC-CNTs formed disordered clusters, whereas the RR-CNT developed birefringent liquid-crystal domains. Under capillary flow, RRC clusters preferentially accumulated and stacked, while RR domains predominantly slid past one another. Correspondingly, the RRC-CNT dispersions exhibited a type I → IV → III large-amplitude oscillatory shear transition, whereas the RR-CNT showed a type I → III transition. Despite other structural differences among the CNTs, these systematic trends support the RR/RRC distinction as a useful framework beyond conventional persistence-length-based classification.