Correlation between Molecular Structure and Interfacial Properties of Edge or Basal Plane Modified Graphene Oxide

Although graphene oxide (GO) has been reported to be able to be edge functionalized or basal-plane functionalized separately, no research has been done on comparing both the molecular structure and interfacial properties of them. In this study, an alkyl amine was grafted to the epoxy group on the basal planes of GO (b-GO) and carboxyl group at the edges of GO (e-GO) separately by using different synthetic approach. With the combination of various molecular structure and morphology characterization methodologies, we proved that the reaction site for e-GO was only with the carboxyl group at the edge of GO and that for b-GO was epoxy group on the basal plane of GO, indicating that GO could be controllably functionalized (fGOs), and the structure of fGOs could be tuned. Study of the interfacial behavior of fGOs at liquid–liquid interface showed that the interfacial tension reducing capability of e-GO was broader than that of b-GO, and for alkyl oil phase, b-GO was slightly better than e-GO, and both were better than traditional nonionic surfactant. Study of the interfacial behavior of fGOs at liquid–solid interface demonstrated that, after absorption, b-GO arranged vertically on the metal surface, forming dense, compact, and strong film, while e-GO aligned horizontally to form loosely assembled film, resulting in higher interfacial shear strength than that of b-GO. Our results indicate the possibilities for tuning the interfacial properties of GO at both liquid–liquid and liquid–solid interfaces, which may be promising in the potential applications in controlled drug delivery, surface protection, absorption and separation, lubrication, nanocomposite, and catalyst fields.