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Substrate Wettability Influences Internal Jet Formation and Mixing during Droplet Coalescence
Thomas C Sykes1, David Harbottle2, Zinedine Khatir3
1EPSRC Centre for Doctoral Training in Fluid Dynamics, University of Leeds, Leeds LS2 9JT, United Kingdom.
Langmuir : the ACS Journal of Surfaces and Colloids
|August 14, 2020
Summary
An internal jet forms during droplet coalescence when capillary waves reflect from the contact line. Substrate wettability, particularly the receding contact angle, significantly influences jet formation and fluid mixing efficiency.
Area of Science:
- Fluid dynamics
- Interfacial phenomena
- Surface science
Background:
- Droplet coalescence is crucial in various industrial processes.
- Understanding internal fluid dynamics during coalescence is key to controlling outcomes.
- Substrate wettability plays a significant role in interfacial dynamics.
Purpose of the Study:
- Investigate the internal dynamics of axisymmetric droplet coalescence.
- Identify mechanisms driving internal jet formation.
- Determine the influence of substrate wettability on coalescence dynamics and fluid mixing.
Main Methods:
- Laboratory experiments using high-speed imaging to visualize internal flows.
- Numerical simulations employing the volume of fluid (VOF) method.
- Quantitative validation of simulations against experimental data using image processing.
Main Results:
- Formation of an internal jet driven by reflected capillary waves and droplet curvature.
- Jet formation is critically dependent on substrate wettability, especially the receding contact angle.
- Regime maps show enhanced jet formation with increasing receding contact angle and decreasing viscosity.
Conclusions:
- Substrate wettability is a key parameter controlling internal jet formation during droplet coalescence.
- Appropriate wettability can enhance fluid mixing efficiency, even at varied droplet volume ratios.
- The study provides insights into optimizing coalescence processes for improved mixing.
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