Fluid Flow Measurements in Nanoslits Using Holographic Microscopy.

Area of Science:

• Nanofluidics
• Microscopy
• Fluid dynamics

Background:

• Observing and measuring fluid motion at the nanoscale is crucial for developing on-chip biomedical and chemical applications.
• Existing methods face challenges in accurately capturing flow dynamics in confined nanofluidic environments.

Purpose of the Study:

• To introduce a novel high-speed digital holographic microscopy technique for measuring both slow and fast fluid flows in nanofluidics.
• To characterize evaporation-driven and surface acoustic wave-driven flows within nanoslit channels.

Main Methods:

• High-speed digital holographic microscopy was employed to visualize and quantify fluid motion.
• Measurements were conducted in nanoslit channels of 25 nm and 7 nm heights.
• A noise reduction process, including spatial averaging, was developed and applied.

Main Results:

• Evaporation-driven flow in 7 nm and 25 nm nanoslits was found to be approximately 15 times slower than in open atmospheric conditions due to geometric confinement.
• Surface acoustic wave-driven flow was measured at 0.12 m/s in a 25 nm channel, resulting from 39.7 MHz acoustic wave-fluid interaction.
• Spatial averaging proved effective in discerning fluid flow and dewetting phenomena within the nanoslit channels over time.

Conclusions:

• The developed high-speed digital holographic microscopy method enables precise measurement of fluid dynamics in nanofluidics.
• Nanoslit confinement significantly impacts evaporation-driven flow rates.
• Acoustic wave-fluid interactions can drive measurable flow within nanofluidic devices.