Transition of Graphene Oxide from Nanomembrane to Nanoscroll Mediated by Organic Solvent in Dispersion

Morphological transition of two-dimensional (2D) nanomembranes, where multiple factors such as thermal fluctuation, wrinkling, crumpling, and the intersheet adhesion play competitive roles, is a fascinating and intriguing problem with both fundamental and applied interests. In this work, we find that the morphological transition from graphene oxide (GO) nanomembranes to nanoscrolls can be mediated by N,N-dimethylformamide (DMF) in DMF-H2O dispersions. As the DMF content is in the range from 30 vol % to 100 vol %, GO membranes are rolled up to form nanoscrolls in the low GO concentration regime (<0.05 mg/mL). The formed GO nanoscrolls show features of tight rolling-up with interlayer distance of 0.62 +/- 0.04 nm and tubular structure with inner diameter of 5 nm. This morphological transition is proved to be controlled by the surface negative charges of the GO membranes in the dispersions. The electric double layer interaction, which hinders nanoscroll formation by introducing an electrostatic potential barrier in the scrolling nucleation and electrostatic repulsion between adjacent layers in the overlapping region during the rolling-up process, is significantly reduced by DMF. Theoretical analysis identifies the scrolling pathway through the energy barrier by considering the van der Waals interaction, electrostatic repulsion, elastic resistance of the membranes, and steric exclusion. A theoretical model that can predict the morphological phase diagram of GO in the space of the DMF content and GO concentration is established, which is essential to further explore the GO scroll formation in the dispersions for fundamental and applied researches.