Graphene is a novel 2D carbon material that has numerous applications for energy storage and tissue and organ engineering. However, the dispersion of graphene powder in a fluid medium is challenging because it can be difficult to disperse the lightweight powder particles and prevent them from forming agglomerates or sediments during storage or processing. Several methods can be used to disperse graphene. Some of the methods include chemical and/or mechanical exfoliation of graphite into graphene particles containing between five and twenty atomic layers of carbon.
The dispersion of graphene is mainly dependent on the solvents and the surface tension and solubility parameters of the graphene and the solvent . A good graphene dispersion is achieved when the solute-solvent system divides intermolecular interactions into three components: dispersive (D), polar (P), and hydrogen bonding (H) components.
For preparing stable graphene dispersions, solvents should have similar surface tension and solubility parameters to the graphene. A good graphene dispersion is obtained when the solvent has the following parameters: dD = 18.0 MPa1/2, dP = 9.3 MPa1/2, and dH = 7.7 MPa1/2.
Some of the solvents that can disperse graphene well are water, ethanol, and dimethyl terephthalate. Moreover, these solvents have good thermal properties and lubricity. The dispersibility of graphene is further improved when a surfactant is added to the solvent.
Stable graphene dispersions can be prepared using different solvents with a few surfactants in a short sonication time. Various nitrogen-based surfactants were tested in aqueous, alcoholic, and DCM mediums to determine their stability and exfoliation ability. Among them, PVP-b-PEG and PTFEMA-b-PVP show excellent dispersion in both aqueous and alcoholic mediums.