The influence of various factors on the transition of the fluorinated graphene wettability from superhydrophilicity to high hydrophobicity

Abstract

The wettability of fluorographene has been experimentally and theoretically investigated. The obtained results of modeling the contact angle using molecular dynamics are consistent with the experiment. Fluorographene is a high-quality insulator. The 2D insulator may be used as the atomically thin tunnel barrier. The interaction of fluorographene with water results in the formation of hydroxyl groups. Properties of hydroxofluorographene G(OH)F or Cn(OH)yFx imply temperature antiferromagnetic ordering. Previously it was assumed that complete fluorination leads to high hydrophobicity. The authors of this paper have shown that prolonged fluorination, on the contrary, induces superhydrophilicity. The adsorption of hydrocarbons from the ambient air onto the fluorographene surface results in high hydrophobicity. The combined effect of adsorbed hydrocarbons and nano-micro texturing of the surface due to fluorination allows for the transition to superhydrophobicity. After long-term storage of fluorographene in the air for 6 months, the fluorine content (in contrast to other works) has decreased slightly (by less than 10 %). Fluorine is present at a temperature of 250–300 °C in a hydrogen atmosphere. Stable C1F8.5 complexes have been obtained for the first time as a result of the self-organization of dome-shaped surface structures during prolonged fluorination. It is assumed that part of the fluorine (C1F1) has a covalent or ionic bond, and the rest of the fluorine molecules are arranged in a closed framework surrounded by C atoms. Usually, complete fluorination of graphene leads to a ratio of C1Fn less than 1 (maximum value n = 1–1.1). Dome-shaped structures with an external carbon backbone may be used for gas storage. It is possible to control the properties of fluorographene and ensure the transition from superhydrophilicity to superhydrophobicity.