Generation and Observation of Long-Lasting and Self-Sustaining Marangoni Flow

Area of Science:

• Fluid Dynamics
• Surface Chemistry
• Physical Chemistry

Background:

• Evaporation-induced concentration gradients can cause surface tension gradients, leading to fluid convection (Marangoni effect).
• Understanding and controlling these interfacial flows is crucial for various applications.

Purpose of the Study:

• To demonstrate and characterize Marangoni flow induced by ethanol in concentrated sodium hydroxide solution.
• To investigate methods for controlling and sustaining this flow.

Main Methods:

• Particle image velocimetry (PIV) to measure interfacial speeds.
• Gravimetric analysis to monitor evaporation rates.
• Introduction of impermeable objects to create stationary concentration gradients.

Main Results:

• Minute ethanol concentrations ( < 0.5 mol %) in NaOH solutions induce pronounced, long-lasting Marangoni flow upon evaporation.
• Interfacial speed increases with evaporation rate for low ethanol concentrations.
• Stationary flows can be controlled by object shape, demonstrating efficient energy conversion to kinetic fluid energy.
• Effect is suppressed in lower NaOH concentrations due to limited ethanol dissolution in bulk.

Conclusions:

• Ethanol in concentrated NaOH solutions can generate self-sustaining Marangoni flows due to efficient surface accumulation and replenishment.
• Contact-free control of interfacial flows is achievable through engineered concentration gradients.
• The system highlights efficient energy conversion from evaporation to fluid motion.