Hydrocarbons enhanced generation of surface nanobubbles by ethanol-water exchange

Abstract

The ethanol-water (E-W) exchange at the graphite surface is a convenient method for creating surface nanobubbles due to its high efficiency and repeatability. However, understanding and controlling the nucleation dynamics remain challenging. While the formation of interfacial gas entities is usually attributed to the differences in gas solubility, alterations in surface properties resulting from the exchange process cannot be ignored. Herein, we investigated how varying hydrophobicity of the graphite surface during the E-W exchange affects the efficient production of surface nanobubbles. Observations demonstrated that the presence of ethanol could significantly enhance the generation of surface nanobubbles compared to the exchange without ethanol. Contact angle measurements and C-H vibrational spectra revealed that the absorbed hydrocarbon from the ethanol enhances surface hydrophobicity. We observed the volume shrinkage of nanobubbles and partial removal of the gas-like layer that supports bubbles in degassed water. Based on these results, we proposed that the absorbed hydrocarbon from ethanol makes the substrates with higher hydrophobicity during the E-W exchange, which may contribute to the formation of a gas enrichment layer that is beneficial to nucleation and stabilization of surface nanobubbles above it. The findings will provide valuable insights into the nucleation process of interfacial gas domains and their stabilization on hydrophobic surfaces, further advancing the controllable generation of surface nanobubbles.