Yield stress, thixotropy and shear banding in a dilute aqueous suspension of few layer graphene oxide platelets

Abstract

We demonstrate a rigidity percolation transition and the onset of yield stress in a dilute aqueous dispersion of graphene oxide platelets (aspect ratio ∼5000) above a critical volume fraction of 3.75 × 10⁻⁴ with a percolation exponent of 2.4 ± 0.1. The viscoelastic moduli of the gel at rest measured as a function of time indicate the absence of structural evolution of the 3D percolated network of disks. However a shear-induced aging giving rise to a compact jammed state and shear rejuvenation indicating a homogenous flow is observed when a steady shear stress (σ) is imposed in creep experiments. We construct a shear diagram (σ vs. volume fraction ϕ) and the critical stress above which shear rejuvenation occurs is identified as the yield stress σ_y of the gel. The minimum steady state shear rate _m obtained from creep experiments agrees well with the end of the plateau region in a controlled shear rate flow curve, indicating a shear localization below _m. A steady state shear banding in the plateau region of the flow curve observed in particle velocimetry measurements in a Couette geometry confirms that the dilute suspensions of GO platelets form a thixotropic yield stress fluid.