On the Solvation Behavior of Graphene Oxide in Ethylene Glycol/Water Mixtures

Abstract

The self-association and solvation pattern of graphene oxide (GO) in water, ethylene glycol (EG), and their mixtures were analyzed by means of UV/Vis spectrophotometry. A careful analysis of the absorbance dependencies vs. the GO concentration shows that self-association of the GO sheets in EG occurs at higher concentration compared to that in water. It was established that depending on the mixed solvent composition, two different types of the GO solvates are formed. The results of quantum chemical calculations allow one to suggest that in the water-rich compositions, the GO oxygen-containing groups are in direct contact with water molecules while in the glycol-rich media the EG molecules fully substitute water in the GO's first solvation layer.

Macroscale Superlubricity Enabled by the Synergy Effect of Graphene-Oxide Nanoflakes and Ethanediol

“…EDO and water can associate with GONFs via hydrogen-bond interactions occurring within the first GONF layer as previously mentioned. 37,38 Because our previous work demonstrates that hydrated networks are able to provide a super-low frictional forces even between dissimilar friction pairs, 47 it is reasonable that hydrated GONFs−EDO networks play an important in the reduction of liquid shear stress in this study. Therefore, the low friction in the liquid-contact region mainly stems from the relative low shear stress at the EDO−GONF interface and between hydrated GONF and EDO networks.…”

“…When compared against Figure c, it can be observed that the interlayer spacing of GONFs remains unchanged after the prior rubbing motion. However, thicknesses of adsorbed GONFs after rubbing were observed to be larger compared to those of original GONFs, thereby indicating that GONFs in EDO solution might gather to form a thicker, adsorbed layer on friction surfaces subjected to rubbing motion . This provides better protection to surfaces against direct contact.…”

“…Therefore, a slight shift in the Raman spectrum of GONFs–EDO solution can be observed after drying. An extant study has demonstrated that in a water-rich solution (original GONFs–EDO solution), GONFs could be covered by water molecules via action of oxygen-containing groups, whereas the solution tends to become EDO-rich during drying, and EDO tends to substitute water, thereby forming the GONF solvate on the first layer. Therefore, the observed shift in Raman spectrum can be attributed to variations in the solvate formed via hydrogen bond interactions …”

“…However, thicknesses of adsorbed GONFs after rubbing were observed to be larger compared to those of original GONFs, thereby indicating that GONFs in EDO solution might gather to form a thicker, adsorbed layer on friction surfaces subjected to rubbing motion. 37 This provides better protection to surfaces against direct contact. A major benefit of GONF adsorption on friction surfaces corresponds to the improvement in the anti-wear property of a lubricant.…”