Long-Term Stability of Surface Nanobubbles in Undersaturated Aqueous Solution

Area of Science:

• Surface science
• Physical chemistry
• Nanotechnology

Background:

• Surface nanobubbles are theoretically unstable, yet experimentally observed to persist for extended periods.
• The discrepancy is often attributed to the pinning of the three-phase contact line.
• Existing models propose solution oversaturation and surface pinning as key stabilization factors.

Purpose of the Study:

• To experimentally investigate the effect of solution saturation on surface nanobubble stability.
• To challenge the prevailing theory that nanobubble stability relies solely on pinning and oversaturation.

Main Methods:

• Nucleating surface nanobubbles on hydrophobic surfaces using two distinct methods.
• Characterizing nanobubbles via Atomic Force Microscopy (AFM).
• Systematically altering solution saturation by exchanging the surrounding liquid with partially degassed water using two techniques.

Main Results:

• Surface nanobubbles demonstrated stability for hours even in undersaturated solutions.
• Experimental lifetimes were compared against theoretical calculations for pinned nanobubbles in undersaturated conditions.
• Observed stability in undersaturated conditions contradicts the pinning mechanism as the sole explanation for long-term stability.

Conclusions:

• The long-term stability of surface nanobubbles is not solely explained by the pinning mechanism.
• Solution undersaturation plays a significant role in stabilizing surface nanobubbles, contrary to established theories.
• Further research is needed to fully understand the mechanisms governing surface nanobubble persistence.