Ultrahigh concentration exfoliation and aqueous dispersion of few-layer graphene by excluded volume effect

Colloidal properties of nanoparticles are intricately linked to their morphology. Traditionally, achieving high-concentration dispersions of two-dimensional (2D) nanosheets has proven challenging as they tend to agglomerate or re-stack under increased surface contact and Van der Waals attraction. Here, we unveil an excluded volume effect enabled by 2D morphology, which can be coupled with electrostatic repulsion to synthesize high-concentration aqueous graphene dispersions. To achieve this, we designed a sequential process involving edge oxidation, bubble expansion and mechanical shearing, through which graphite flakes were exfoliated into aqueous dispersions with ~94.5 wt.% yield of few-layer graphene, high concentration exceeding 100 mg mL-1, long-term stability over ~550 days, and large-scale wet processability. Structural analysis and theoretical modeling suggested that the 2D morphology of the resultant graphene nanosheets facilitates inter-sheet repulsive excluded volume interactions, leading to a fractal jammed network structure composed of nanosheets and tactoids to prevent their agglomeration. This effect was further leveraged in a continuous stirred tank reactor for the pilot-scale production of concentrated graphene dispersions. Our study unveils the role of excluded volume effect in stabilizing 2D-material colloids for industrial production and processing. The large-scale synthesis of high-concentration dispersions of 2D nanosheets remains challenging. Here, the authors report a multi-step process to produce aqueous dispersions of few-layer graphene with ~94.5 wt.% yield and concentrations exceeding 100 mg/mL, showing the important role of inter-sheet repulsive excluded volume interactions.