Ionic adsorption on bulk nanobubble interfaces and its uncertain role in diffusive stability

Area of Science:

• Physical Chemistry
• Nanotechnology
• Computational Science

Background:

• Bulk nanobubbles are proposed for applications like water treatment and theranostics.
• Their long lifetimes contradict classical bubble dynamics, with electrostatic stability as a leading hypothesis.
• Experimental observations of negative zeta potentials support the electrostatic mechanism.

Purpose of the Study:

• Investigate the electrostatic stability mechanism of bulk nanobubbles.
• Model ionic adsorption and zeta potential at the liquid-gas interface using simulations.
• Critically examine the role of electrostatic stress in nanobubble longevity.

Main Methods:

• High-fidelity Molecular Dynamics simulations.
• Modeling bulk nanobubbles in sodium iodide electrolyte solution.
• Analysis of ionic adsorption and electric double layer (EDL) formation.

Main Results:

• Simulations confirm ion adsorption and EDL formation, consistent with experimental zeta potential measurements.
• No significant electrostatic stress was found acting on the nanobubble surface.
• Internal gas pressure is accurately predicted by the Laplace pressure equation, even with Tolman length correction.

Conclusions:

• The proposed electrostatic stress mechanism does not appear to stabilize bulk nanobubbles against dissolution.
• Water molecule rearrangement neutralizes ion charge density within the EDL.
• Alternative mechanisms for nanobubble stability require further investigation.