Study of liquid jet instability by confocal microscopy.

Area of Science:

• Fluid Dynamics
• Surface Science
• Optical Metrology

Background:

• Accurate measurement of dynamic surface tension is crucial for understanding liquid behavior.
• Traditional methods often struggle with the rapid timescales (<1 ms) relevant to microjet instability.
• Confocal microscopy offers high spatial resolution for dynamic surface analysis.

Purpose of the Study:

• To develop and validate a confocal microscopy technique for measuring dynamic surface tension.
• To investigate liquid microjet instability at early surface ages (≤1 ms).
• To determine the dynamic surface tension of water and ethanol/water mixtures.

Main Methods:

• Utilized laser beam reflection and confocal microscopy to analyze liquid microjet oscillations.
• Achieved radial resolution of 4 nm and surface position accuracy of 0.2 μm.
• Measured growth rates of periodically perturbed water and ethanol/water jets (100-μm nozzle, 5.7 m/s velocity).

Main Results:

• Successfully measured dynamic surface tension from jet instability growth rates using a linear model.
• Quantified oscillation amplitudes at early stages (≤1 ms) with high precision.
• Synchronized confocal imaging with jet perturbation to study temporal evolution of jet structures.

Conclusions:

• The confocal microscopy method enables precise dynamic surface tension measurements at microsecond timescales.
• This technique provides insights into the fundamental physics of liquid microjet evolution.
• The study demonstrates a robust approach for characterizing dynamic interfacial properties.