Innovations in next-generation batteries, solar cells, touch screens, and supercapacitors may hinge on easily obtainable graphene. A study published in The Journal of Chemical Physics assesses liquid solvents for their potential to convert (bulk crystalline) graphite to graphene.

While previous work shows that graphene can be extracted from graphite using liquid-phase exfoliation, additional measurements and modeling are necessary to describe the solvents’ behavior at an interface with graphite. Investigators characterized a number of potential liquid solvents to determine which has the smallest solid-liquid interfacial energy when in contact with graphite. For ionic liquids, this translates into solvents with high surface tension and small contact angle.

The authors measured surface tension and contact angle for 16 ionic liquids and three molecular liquids. Ionic liquids based on planar aromatic imidazolium (C3N2H4) ring structure, derivatized with one or two pendant aromatic rings, distinguished themselves from the group by their high surface tension and a contact angle of zero. They compared careful experimental measurements from all the solvents with computer simulations using the Molecular Dynamics method to determine the solvent behavior when in contact with graphite. These simulations showed that at this interface, ionic liquids with long alkyl side chains are more ordered than other candidate solvents.

Looking at ionic liquids within a range of surface tensions thought to make them promising exfoliants, the authors discovered they were not always those with the lowest liquid-graphite interfacial energies. The key result emphasized by the authors is that the interfacial energy between the ionic liquid and graphite may be a more useful metric for designing processes to exfoliate and stabilize high concentrations of graphene.

Source: “Ionic liquids at the surface of graphite: Wettability and structure,” by Emilie Bordes, Laurent Douce, Edward L. Quitevis, Agilio A. H. Padua, and Margarida Costa Gomez, The Journal of Chemical Physics (2018). The article can be accessed at