Aqueous dispersions of highly conductive carbon nanomaterials: Unusual aggregation mechanism

Abstract

Determination of the optimal conductive composition and operational flow conditions are of profound significance for aqueous–based semisolid flow battery and supercapacitor applications. We systematically investigated the development of equilibrium microstructure and flow–induced structural transitions in aqueous dispersions of carbon black (CB) in 1 M LiNO3 at 25 °C. Simultaneous measurements of the impedance spectra and optical texture distinguished two unique percolated dispersions with distinct microstructure and aggregation mechanisms around a critical CB content: CCB = 4 wt%. A tenuous network of weakly–linked aggregates with rapid diffusion–limited aggregation mechanism (DLA) is formed at CCB < 4 wt%. A compact network of strongly fused aggregates with slow reaction–limited aggregation mechanism (RLA) dominates the dispersion microstructure above the critical CCB. The percolated dispersions commonly exhibited a three–regime (two thinning separated by thickening regime) flow curve consistent with structural breaking up (conductivity loss) and alignment of flowing units (conductivity recovery) at a critical shear rate that pertain to CCB.