Filling the gap between transient and steady shear rheology of aqueous graphene oxide dispersions
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Even though the rheological behavior of aqueous graphene oxide (G-O) dispersions has been shown to be strongly time-dependent, only few transient measurements have been reported in the literature. In this work, we attempt to fill the gap between transient and steady shear rheological characterizations of aqueous G-O dispersions in the concentration range of 0.004 < ϕ < 3.5 wt%, by conducting comprehensive rheological measurements, including oscillatory shear flow, transient shear flow, and steady shear flow. Steady shear measurements have been performed after the evaluation of transient properties of the G-O dispersions, to assure steady-state conditions. We identify the critical concentration ϕ c = 0.08 wt% (where G-O sheets start to interact) from oscillatory shear experiments. We find that the rheology of G-O dispersions strongly depends on the G-O concentration ϕ. Transient measurements of shear viscosity and first normal stress difference suggest that G-O dispersions behave like nematic polymeric liquid crystals at ϕ/ϕ c = 25, in agreement with other work reported in the literature. G-O dispersions also display a transition from negative to positive values of the first normal stress difference with increasing shear rates. Experimental findings of aqueous graphene oxide dispersions are compared and discussed with models and experiments reported for nematic polymeric liquid crystals, laponite, and organoclay dispersions.
KeywordsGraphene oxide Liquid crystals 2D suspensions 2D dispersions Normal stress Rheology
The authors thank Dr. Steven Aird for careful proof reading. The authors also thank Prof. Pier Luca Maffettone, Prof. Giovanniantonio Natale, and Prof. Gareth McKinley for helpful discussions. F.D.G. and A.Q.S. gratefully acknowledge the support of the Okinawa Institute of Science and Technology Graduate University with subsidy funding from the Cabinet Office, Government of Japan. B.V.C. and R.S.R were supported by IBS-R019-D1.
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