Effect of functional groups on crumpling behavior and structure of graphene oxide

Abstract

Graphene has a wide range of applications in the fields of electricity, chemistry, biomedicine, and lubrication. But the strong van der Waals interaction between graphene sheets makes it easy to aggregate in preparation process, difficult to produce and put into practical applcation on a large-scale. There are many methods to prevent the graphene sheets from aggregating, such as reducing the size of sheets, adjusting the interaction between solvent and graphene, and using dispersant. Another possible method is to turn the sheet graphene into a three-dimensional structure like the crumpled paper. Compared with sheet graphene, the crumpled graphene ball has excellent aggregation-resistant. The current research on crumpled graphene ball mainly focuses on the effect of the initial structure of graphene sheet on the structure stability of the crumpled ball, but rarely involves the effect of functional groups. In this paper, ReaxFF molecular dynamics is used to simulate the crumpling process of graphene oxide sheet. The effect of functional groups (hydroxyl, epoxy) on the crumpling behavior and the stability of the crumpled ball of graphene oxide are studied. Graphene sheet oxidized by hydroxyl exhibits a push-up crumpling behavior. Graphene sheet oxidized by epoxy exhibits a layer-to-layer fitted crumpling behavior. Different crumpling behavior will lead to the difference in final crumpled ball structure. By analyzing the relationship between the atomic level potential energy incremental distribution and the distribution of broken and formed C—C bonds, we find that the broken and formed C—C bonds mainly occur in areas with a large degree of deformation, and the epoxy group has a stronger weakening effect on the C—C bond connected to it than the hydroxyl group. The release process of graphene oxide crumpled ball is simulated to study its structural stability. The stability of graphene oxide crumpled ball depends on the number of the broken and formed C—C bonds, that is, the more the number of broken and formed C—C bonds, the more stable the structure is, and under the same oxidation rate, the stability of the crumpled ball structure increases with the proportion of epoxy groups increasing. This study shows that the stability of graphene oxide crumpled ball structure can be controlled by changing the relative proportion of functional groups.