Prying or pushing? The dispersion mechanism of amphiphilic molecules on graphene in aqueous solution: A molecular dynamics simulation

Abstract

Amphiphilic molecule aqueous solutions are widely used in the dispersion of graphene. Previous experimental studies have focused on selecting amphiphilic molecules with high dispersion yield and stability through a large number of “trial and error” methods, without delving into their dispersion mechanism. In this study, the graphene dispersing processes in aqueous solutions of three amphiphilic dispersants with different structures, flavin mononucleotide sodium, polyvinyl pyrrolidone and the oligomer of poly(pyrenemethyl acrylate)-b-poly[(polyethylene glycol) acrylate], were investigated by molecular dynamics simulation. By characterizing the influence of three dispersants on the intercalation effect of water molecules, their distribution relative to graphene, and their influence on the equilibrium conformation of graphene, the simulation conclusion was drawn that the arrangement of hydrophilic and hydrophobic structures of amphiphilic molecules is the decisive factor in their mechanism of dispersing graphene. Two different dispersion mechanisms have been concluded and the relationship between them and the structure of amphiphilic molecules was elaborated. This article also explored the driving forces of two mechanisms and the influence of graphene lateral area on the dispersion effectiveness. This investigation provided theoretical clues to design the amphiphilic molecules with suitable structure and select appropriate mechanical operations to achieve higher dispersion yield.