Study of the Optimization of Hansen Solubility Parameters in the Ultrasonic Exfoliation Technique to Achieve Stable Graphene Dispersions

Abstract

Graphene synthesis by ultrasonic exfoliation of graphite in organic solvents yields good concentrations of graphene dispersions. This technique is extremely versatile, economical and environmentally friendly. The technique depends on the matching of the surface energy of graphite and solvent which can also be expressed through Hansen solubility parameters (HSP). HSP refers the three parameters, δD for dispersion (van der Waals), δP for polarity (related to dipole moment) and δH for hydrogen bonding. The matching of surface energy is related to minimizing the HSP deviation, R_a. The R_a can be modified by mixing two solvents. According to HSP theory, a decrease in R_a leads to an increase in solubility. Hence maximum solubility should be achieved at minimum R_a. In this study, exfoliation of graphite was performed using a binary solution of low boiling point solvent i.e., isopropyl alcohol (IPA) and water. The theoretical calculations were performed using HSP theory with variation of IPA content in deionized water 0% to 100% v/v with 20% increments. In the experimental part, dispersions were characterized for turbidity and stability. The quantification of dispersions was done by UV-Vis spectroscopy. The experimental results were found to be consistent with the theoretical studies and maximum dispersion was obtained at the minimum value of R_a. The study confirms that the tailoring HSP technique could give better dispersions in binary solutions with optimized mixing ratios and could be used for the scalable production of graphene using numerous binary solvent mixtures.