Hemispherical nanobubbles reduce interfacial slippage in simple liquids.

Area of Science:

• Physics
• Surface Science
• Nanotechnology

Background:

• Nanobubbles are typically expected to increase resonance frequency due to low density and liquid slippage.
• Previous studies have not fully explained the observed negative frequency shifts in nanobubble systems.

Purpose of the Study:

• To investigate the anomalous negative frequency shift caused by nanobubbles.
• To elucidate the underlying physical mechanisms governing nanobubble behavior on surfaces.
• To explore the implications for surface drag in fluid dynamics.

Main Methods:

• Electrochemical quartz crystal microbalance (EQCM) for nanobubble generation and frequency measurement.
• Analysis of resonance frequency shifts in response to nanobubble formation.
• Finite element method (FEM) simulations to model nanobubble interactions and fluid dynamics.

Main Results:

• Observed negative frequency shifts, indicating increased hydrodynamic thickness and reduced slippage.
• Demonstrated that Laplace pressure effects can dominate viscous drag for small, stiff nanobubbles.
• Showed that nanobubbles with a contact angle around 90° can behave like a solid film, increasing surface drag.

Conclusions:

• Laplace pressure plays a crucial role in nanobubble behavior, leading to unexpected hydrodynamic effects.
• Nanobubble stiffness and arrangement influence their impact on surface properties and fluid flow.
• The findings have implications for understanding surface drag in micro/nanofluidic devices and other applications involving nanobubbles.