In this work, the dispersion behavior of graphene oxide (GO) nanosheets in water was studied by a series of MD simulations for water, GO, and the water/GO mixed systems. The simulation results showed that the water/GO system has a well-ordered structure with strong H-bond interactions. The initial value (4.0 A˚) of the interlayer distance between two GO sheets at the beginning of the simulation clearly increased (rv7.2 A˚) in the presence of water as compared to its value after simulation in the absence of water (5.7 A˚). The solubility parameter of GO was calculated as a function of both temperature and number of layers. The solubility parameter of GO at 300 K reached a plateau at 44.9 MPa1/2 when the number of layers was five. Hence, water is a good solvent for dispersing GO since their solubility parameters are close to each other especially at temperatures close to the freezing point of water. The strong H-bond between water and oxygen-functional groups of GO makes the enthalpy favorable to form stable GO dispersions in water.

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