Nanobubble boundary layer thickness quantified by solvent relaxation NMR

Area of Science:

• Interface science
• Nanotechnology
• Physical chemistry

Background:

• The unusual stability of nanobubbles in solution is linked to their boundary layer.
• Characterizing this boundary layer is challenging due to its dynamic nature and difficulty differentiating from bulk water.
• Sensitive interface analysis is needed to study water molecules at the interface versus in the bulk.

Purpose of the Study:

• To quantitatively determine the mechanical and structural properties of the nanobubble boundary layer.
• To investigate the boundary layer using sensitive interface analysis technologies.
• To differentiate interfacial water from bulk water.

Main Methods:

• Employed in-situ and non-deconstructive solvent relaxation nuclear magnetic resonance (NMR).
• Measured relaxation rates and thickness of water in the boundary layer.
• Determined the ratio of interfacial water molecules to bulk water molecules and boundary layer thickness.

Main Results:

• The spin-spin relaxation time of water in the boundary layer was two orders of magnitude lower than free water.
• Determined boundary layer thickness ranged from 35-45 nm, representing 17.0%-8.7% of nanobubble size.
• Boundary layer thickness increased as nanobubble diameter decreased.

Conclusions:

• Established a quantitative measurement model for the nanobubble boundary layer.
• The findings provide insights into interfacial properties and the stabilization mechanism of bulk nanobubbles.
• Solvent relaxation NMR is effective for characterizing nanobubble boundary layers.