Liquid repellency from graphite sheets with different oxidation levels

This study investigates the influence of oxidation level on the repellency toward water and ethylene glycol (EG) droplets on oxidized graphite sheets. Thermal treatment is adopted to adjust oxidation extent and distribution of oxygen functionalities on graphite oxide (GO) sheets. The O/C ratio displays a negative effect on liquid repellencies on the resulting GO sheets. The GO sheet with the lowest O/C ratio (~ 8%) shows the maximal contact angles (CAs) of water and EG: 143.2° and 135.2°, respectively. A linear plot of the ratio of CH and CC groups versus CAs of water and EG droplets proves that the number of hydrophobic groups strongly raises the hydrophobic fraction of graphene sheets against the wetting of polar liquids. Additionally, it can be found that only ~ 54% hydrophobic fraction of GO sheets cannot completely repel the wetting. This finding offers a major benefit in (i) simulating the critical point for the total wetting phenomenon and (ii) enhancing the hydrophobic performance on GO sheets. With the results as basis, this study offers fundamentals on the water and EG repellency of GO surfaces with different oxidation extents.

► Influence of oxidation level on liquid repellency on graphite sheets is investigated.
► A linear plot of the ratio of CC groups versus contact angle can be obtained.
► The O/C ratio displays a negative effect on liquid repellency on graphite sheets.
► This study offers fundamentals on liquid repellency of graphite oxide surface.