Influence of dispersion medium on thermodynamic parameters of natural graphite exfoliation for manufacturing graphene-based suspensions

In the present study, we report the calculated value of surface energy for liquid-phase exfoliated few-layer graphene platelets based on experimental data for contact angles of graphene-based films. Free mixing energies were calculated via direct technique from data on surface tensions and their temperature coefficients, as well as using Hansen solubility parametersto obtain Flory-Huggins constants. Although the values obtained for different methods vary, qualitatively it was shown that colloidal systems based on few-layered graphene platelets are lyophobic, and freeenergies for ethylene glycol, diethylene glycol and N-methylpyrrolidone are all close and far lower than that for water. For ethylene glycol-based suspension assessment of the structure via transmission electron microscopy and Raman spectroscopy was performed. Polyols were shown to be very promising media for dispersion and exfoliation of natural graphite to manufacture graphene of high structural quality, effective wetting and stabilization of the free surface at low free energy of mixing values. Calculated values of thermodynamic functions can be used in developing new graphene manufacturing technologies based on direct exfoliation and subsequent stabilization of the newly formed free surface.