How to obtain high monolayer content in liquid phase exfoliation of graphene: A molecular dynamic simulation

Monolayer is strong required in many fields of graphene-application, further insights into the efficient path of obtaining high monolayer content in liquid phase exfoliation of graphene are essential to explore it as a more potent alternative to chemical vapor deposition. Here, dynamic processes of shear exfoliation and narrow sense of liquid phase exfoliation in pure solvent and mixture solvent were investigated using molecular dynamics (MD) simulations to summarize an exfoliation scheme to obtain high monolayer content. By calculating the amount of shear force required for shear exfoliation, it has been found the requirement for the velocity gradient of solvent to monolayer graphene is 1011–1012 s−1, leading to a monolayer content of nearly 0 by shear exfoliation in all kinds of solvents. On the other hand, with solvent-insertion in narrow sense of liquid phase exfoliation, by investigating the influence of tensile force and shear force on gap formation, and the influence of solvent type on solvent-insertion and solvent-monolayer formation and stability, the conditions of high monolayer content has been summarized as follows: rapid insertion of solvent into the sheet interlayers to form solvent monolayer with moderate stability, which could be achieved only through the choice of the type of mixed solvent and the design of the external force applied. The types of mechanical force provided by commonly used mechanical operation were deduced, and in turn it is advised to use low speed agitation and ultrasound simultaneously at the initial phase and only agitation with large speed in the later stage of exfoliation process to obtain high monolayer content. This investigation provides theoretical clues and operational suggestions to obtain high monolayer content in liquid phase exfoliation of graphene and other two-dimensional lamellar materials.