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Volatile Droplets on Water are Sculpted by Vigorous Marangoni-Driven Subphase Flow
Yitan Li1, Yuguang Chen2, Yan Li2
1Center for Soft and Living Matter, Institute for Basic Science (IBS), Ulsan 44919, South Korea.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 10, 2023
Summary
Evaporation of volatile oil droplets on water causes strong Marangoni flow, deforming droplets into finger-like shapes. This flow-induced stress, particularly for thin droplets, dictates their complex, dynamic evolution and eventual breakup.
Area of Science:
- Fluid Dynamics
- Interfacial Phenomena
- Soft Matter Physics
Background:
- Highly volatile oil droplets on water exhibit complex shapes when not in equilibrium.
- Evaporation in unsaturated atmospheres induces Marangoni flow, significantly altering droplet behavior.
Purpose of the Study:
- To experimentally and theoretically investigate the dynamic shape changes of evaporating oil-on-water droplets.
- To understand the role of Marangoni flow in droplet deformation and instability.
Main Methods:
- Experimental observation of droplet shapes on millisecond and submillimeter scales.
- Theoretical analysis using scaling arguments to model fluid dynamics.
- Investigation of single-component and two-component (miscible) oil droplets.
Main Results:
- Marangoni-driven convection stresses droplet edges, leading to finger formation.
- Droplet shape evolution depends on contact angle, thickness, and fluid volatility.
- Two-component droplets form rims and eject smaller droplets via Rayleigh-Plateau instability.
- Microscopic droplets exhibit chaotic shape fluctuations and rupture due to subphase flow.
Conclusions:
- The vigorous flow in the water subphase dictates the intricate shapes of evaporating oil droplets.
- Viscous stress from subphase convection can overcome Laplace pressure, driving significant deformations.
- Droplet morphology is a direct consequence of the interplay between evaporation, Marangoni flow, and interfacial properties.
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