Phase Behavior of Pickering Emulsions Stabilized by Graphene Oxide Sheets and Resins

Graphene oxide is preferable to form stable water-in-oil (W/O) emulsions with crude oil, owing to its exceptional structure, including 1 nm in thickness, several micrometers in diameter, and COOH, OH, C-O, C-O-C, and C=O groups on the surface. The properties of the as-prepared emulsions are strongly dependent on the GO concentrations (C-GO) and volume fraction of water to oil. At a volume ratio of 1:1, the GO dispersions and crude oil can be miscible into stable W/O emulsions accompanying with largely increased viscosity even when the GO concentration reduces to 0.0001%. Notably, when the concentration of GO ranges from 0.005% to 0.01%, the viscosity of W/O emulsions increases to several hundred mPa.s with the increased shear time, which is ascribed to the coalescence of the emulsions under shear. The volume fraction of water in the mixtures (F-W) also affects the phase behavior of the emulsions. At C-GO = 0.0001%, 0.001%, and 0.01%, GO dispersions and crude oil are miscible into one phase completely at F-w < 0.7. In the range between 0.1 and 0.7, viscosity of the emulsion increases as increasing the volume ratio of water to oil. More interestingly, high internal phase emulsions can be obtained in the range of 0.0005-0.008% at F-w = 0.75, in which case viscosity of the emulsions reaches the maximum, i.e., nearly 200 times higher than that of crude oil, due to the high internal phase volume fractions. These results show that the GO dispersions are favorable to form stable W/O emulsions with high internal phase volume fraction, and have a great potential in improving oil displacement efficiency of chemical flooding.