Understanding graphene production by ionic surfactant exfoliation: a molecular dynamics simulation study

We have simulated sodium dodecyl sulfate (SDS) surfactant/waterþbilayer graphene mixture system to investigate two mechanisms of graphene exfoliation: changing the interlayer distance and sliding away the relative distance. By calculating the total energy as a function of the interlayer (sliding-away) distance at different surface-coverage concentrations of SDS surfactant (SDS concentrations), we obtain the separation energy barriers underlying the two mechanisms and their dependence on SDS concentration. Overall, in the first process, the energy barrier can only be reduced by the SDS slightly, which is too big to be viable. While in the second process, the energy barrier can be first decreased continuously with the increasing SDS concentration until it almost completely disappear in the optimal SDS concentration range (1.5-2.0/nm2) and then increase again with the further increase in SDS concentration. Therefore, the second sliding-away mechanism is a more viable separation process. The analysis of SDS anion density profile on the graphene surface indicates that the graphene-surfactant interaction plays an important role in the separation process by stabilizing the separated graphene sheet.