Influence of Adsorption Energy in Graphene Production via Surfactant-Assisted Exfoliation of Graphite: A Graphene-Dispersant Design

It has been reported that the dispersing ability of a given surfactant in surfactant-assisted liquid-phase exfoliation of graphite is extremely affected by its adsorption energy on graphene nanosheets. This study employs computational and experimental techniques to analyze the true relationship between adsorption energy and the dispersing ability of a group of surfactants in the surfactant-assisted liquid-phase exfoliation of graphite. In the first section, adsorption energies computed for a group of homologous surfactants with different hydrocarbon tail lengths are used to predict dispersing-ability trends. It is found that the adsorption energy of the surfactants correlates directly with their tail length. In light of the literature, it is therefore expected that the surfactant with the highest adsorption energy is most effective at dispersing. The experimental section examines this expectation and shows that this is not guaranteed as a general rule. Based on the experimental results, this expectation can be met when surfactant concentrations are quite below surfactants' critical micelle concentrations (CMCs) but fails at concentrations near or exceeding CMCs. Finally, quantum computation and molecular dynamics simulations are employed to justify the dispersing-ability trend observed at higher concentrations. Results demonstrate that the molecular size of the surfactants becomes considerable at these concentrations. In view of this, a new quantity, "adsorption energy per molecular volume", is proposed to explain the behavior of the surfactants at high concentrations. Using this new quantity, the dispersing-ability trend observed at higher concentrations is explained.