Dynamic Viscosity and Surface Tension of Stable Graphene Oxide and Reduced Graphene Oxide Aqueous Nanofluids

This experimental work studies the effect of graphene oxide chemical reduction on the dynamic viscosity and surface tension of water-based nanofluids. Graphene oxide (GO) nanopowder was produced from commercial synthetic graphite through a derived Hummers' method and reduced graphene oxides (rGOs) were chemically reduced from GO by using various concentrations of sodium borohydride. Three different aqueous nanofluid sets were designed using GO and rGOs at nanoparticle volume concentrations ranging from 0.0005 to 0.1%. Shear flow behavior of nanofluids were obtained with a rotational rheometer at temperatures of 20.0 and 30.0 °C and surface tension of nanofluids was studied at 20.0 °C with a drop shape analyzer based on the pendant drop method. rGO nanofluids at 0.1% exhibit lower apparent viscosities and weaker shear-thinning behaviors compared to the corresponding GO nanofluids. For lower concentrations, a Newtonian behavior of nanofluids is reported. Relative viscosity enhancement of nanofluids with nanoparticle content is also modelled by Maron-Pierce's equation. Surface tension is decreased by 3% with increasing nanoadditive loading and without influence of chemical treatment. Such behavior of the prepared graphene-based nanofluids is interesting for the envisaged applications often involving circulating fluids.