Redissolution of Flower-Shaped Graphene Oxide Powder with High Density

As a sort of scalable precursor of graphene, single-layer graphene oxide (GO) has received widespread attention. However, producing dried GO powder which can redisperse in solvents on a molecular level is still under challenge. Here, we have developed a strategy to obtain flower-shaped GO powder (fGO) via a low-temperature spray-drying method. Such GO powder can be redissolved in various solvents including water, with a concentration higher than 3 wt %. The excellent solubility of fGO is totally preserved even after being compressed into a high-density disk (1.26 g/cm(3)). The aqueous solution of fGO can form liquid crystals, which can be assembled into macroscopic graphene papers. By tracking the dissolution process of fGO, we reveal a "swelling-dissociation-stretching" behavior of the GO particles. For the first time, nuclear magnetic resonance (NMR) solution relaxation is applied to in situ monitor the degree of unfolding (DU) of fGO during dissolution. We discover that the classic polymer dissolution mechanism of linear polymer can extend to GO, a two-dimensional macromolecule. Our findings not only provide a solution for the problems in the transportation, storage and applications of GO, but also open a new way to adjust the microstructure of crumpled GO in large scale.