Advances in colloidal rheomechanics for scaled processing of 1D and 2D nanocarbon dispersions

While multi-walled carbon nanotubes (CNTs) have entered early mass production for battery applications, graphene oxide (GO) and single-walled CNTs are facing technical challenges in scaling production. Among various processing approaches, fluid-phase processing is the most promising method for achieving the desired nanocarbon structures at scale. Rheomechanics refers to the study of equilibrium and nonequilibrium thermodynamic states, including static and dynamic stability, and the evolution of microstructure in fluid phase and within solid phase during flow, with short and long-range time scales. Notably, significant advancements have been made in both theoretical and experimental methods to overcome strong van der Waals (vdW) interactions among nanocarbons for stable dispersions and control the microstructures during the fluid processing, drying, and heat treatment—such as electrode coating with GO pastes and wet spinning of CNT dopes. This review summarizes recent advances in the colloidal rheomechanics of highly concentrated dispersions of GO and CNT, whose individual particles exhibit micrometer-scale lateral sizes and lengths, with a focus on colloidal and thermodynamic stability, microstructural evolution, and rheological behavior. In particular, we highlight the role of excluded volume effects in governing these phenomena. The discussion begins with an analysis of attractive and repulsive potentials in GO and CNT dispersions, including modifications and evaluations of vdW, electrostatic, depletion, and excluded volume potentials for achieving colloidal stability in ultra-high-concentration dispersions. In the perspective presented in this review, the extending studies modifying Derjaguin–Landau–Verwey–Overbeek theory to explain the stable state of large-sized nanocarbons are essential for evaluating colloidal stability. In addition, extended studies based on Onsager theory serve as starting point elucidating thermodynamic stability and microstructures at equilibrium, with or without tactoids, as the free energy of 1D and 2D nanocarbon dispersions is primarily influenced by orientational entropy and excluded volume interactions. The perspective also points to the crucial role of excluded volume in the dynamic state, as well as in stability at equilibrium. The review then explores microstructure and orientation evolution during flow, particularly in shear and extensional rheology relevant to processes such as coating and wet spinning. Finally, microstructural evolution is addressed in the context of coagulation, heat treatment, and drying processes, with an emphasis on elasto-capillary effects. By providing an in-depth analysis of these key aspects, this review aims to advance the understanding of colloidal rheomechanics in GO and CNT dispersions, paving the way for improved processing techniques and material performance.