Molecular Dynamics Study of the Aggregation Process of Graphene Oxide in Water

Molecular dynamics (MD) simulations were performed to provide molecular insight into the aggregation process of graphene oxide (GO) in water. The aggregation was found to be a point-line-plane process. Five forces were involved during the process: van der Waals attraction, electrostatic interaction, hydrogen-bond interaction, pp stacking, and the collision of water molecules. The dominant forces were different in the three stages. The connection line was important to the aggregation process and the final overlapping area of the GO aggregate. To study the effect of oxygen content and functional group on the aggregation of GO, four different GOs were used: C10O1(OH)(1)(COOH)(0.5), C30O1(OH)(1)(COOH)(0.5), C10O1(COOH)(0.5), and C10O1(OH)(1) (termed OGO, RGO, GO-COOH, and GO-OH, respectively). RGO aggregated faster than OGO, and GO-OH aggregated faster than GO-COOH. A quantitative analysis showed the difference in aggregation rate of these four GOs should be attributed to the hydrogen bonds. Additionally, the closer GOs were to each other initially, the faster they aggregated. This study reveals the aggregation process of GO and will be helpful in understanding its behavior in water.