Covering surface nanobubbles with a NaCl nanoblanket

Area of Science:

• Surface science
• Nanotechnology
• Physical chemistry

Background:

• Surface nanobubbles are ubiquitous in aqueous environments.
• Understanding their behavior during drying is crucial for surface characterization.
• Salt solutions can influence nanobubble stability and surface morphology.

Purpose of the Study:

• To investigate the effect of sodium chloride (NaCl) concentration on surface nanobubbles during liquid film evaporation.
• To analyze the morphology of salt deposits around nanobubble footprints.
• To explore the potential role of salt layers in nanobubble stabilization.

Main Methods:

• Evaporation of NaCl aqueous solutions (0.01 M and higher) on highly oriented pyrolytic graphite (HOPG) surfaces.
• In-situ observation and post-drying analysis of surface nanobubbles and salt patterns.
• Microscopy techniques to study nanobubble shrinkage and salt flake formation.

Main Results:

• Low NaCl concentration (0.01 M) resulted in incomplete salt film coverage, leaving nanobubble footprints pristine.
• Higher NaCl concentrations led to the formation of a salt blanket covering nanobubbles.
• Upon further drying, this salt blanket cracked and unfolded into flower-like patterns at the nanobubble rim.
• Nanobubbles showed partial stabilization against dissolution when covered by a salt blanket.

Conclusions:

• Surface nanobubbles act as barriers to homogeneous salt film formation.
• The drying process of salt solutions on nanobubbled surfaces creates unique salt morphologies.
• Salt layer formation around nanobubbles may inhibit gas efflux, contributing to their partial stabilization.