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Real-Time Visualization of Solutal Marangoni Convection in Sub-100 nm Precursor Films Using Laser-Generated Droplet
Shinya Hakuta1, Masayuki Naya1, Mamoru Sato1
1Graduate School of Science and Technology, Keio University, 3-14-1, Hiyoshi, Kohoku-ku, Yokohama, Kanagawa 223-8522, Japan.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 17, 2025
Summary
This study introduces a novel tracer-free laser method to visualize fluid flow in ultrathin liquid films. The technique uses laser-induced microdroplets to map nanoscale concentration gradients and interfacial transport.
Area of Science:
- Fluid dynamics
- Nanotechnology
- Surface science
Background:
- Controlling wetting and interfacial transport at the nanoscale is crucial for many applications.
- Existing methods for visualizing flow in ultrathin films have limitations.
Purpose of the Study:
- To develop a tracer-free method for real-time visualization of flow in nanometer-thick liquid films.
- To observe interfacial flow and concentration gradients at the nanoscale.
Main Methods:
- Utilizing a 532 nm continuous-wave laser to generate microdroplets from a binary liquid mixture (ethanol/PEG-200).
- Employing coupled laminar-flow/species-transport simulations to analyze the observed phenomena.
- Using a standard optical microscope for visualization.
Main Results:
- Demonstrated spontaneous generation and controlled movement of PEG-rich microdroplets.
- Identified solutal Marangoni convection as the driving force for surface flow in precursor films.
- Showcased the ability to visualize local concentration gradients by attracting droplets to laser-manipulated regions.
Conclusions:
- The laser-droplet platform offers the first tracer-free technique for observing interfacial flow in precursor films thinner than 100 nm.
- This method surpasses the thickness limitations of conventional micro-PIV (Particle Image Velocimetry).
- Provides new insights into nanoscale transport phenomena and informs the design of heat- and mass-transfer devices.
