Gravitational settling of active droplets
Alexander C Castonguay1, R Kailasham2, Ciera M Wentworth1
1Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
Physical Review. E
|March 18, 2023
Summary
Gravitational settling of oil droplets is influenced by Marangoni forces in micellar solutions. These forces can enhance settling speed and cause lateral motion, unlike in surfactant-free conditions.
Area of Science:
- Fluid dynamics
- Colloid science
- Interfacial phenomena
Background:
- Investigates gravitational settling of oil droplets in aqueous micellar solutions within capillary channels.
- Focuses on active droplets whose motion is governed by a balance of gravitational and Marangoni forces.
Purpose of the Study:
- To understand the interplay between gravitational and Marangoni forces during droplet settling.
- To analyze how varying surfactant concentration, density difference, and viscosity affects droplet motion.
- To characterize the droplet motion decorrelation rate (α) as a function of droplet size.
Main Methods:
- Experimental investigation of oil droplet settling in capillary channels.
- Systematic variation of surfactant concentration, density difference, and continuous phase viscosity.
- Measurement of droplet velocity autocorrelation to determine the decorrelation rate (α).
Main Results:
- Marangoni forces enhance droplet settling speed compared to theoretical predictions for surfactant-free droplets.
- Marangoni forces can induce lateral droplet motion, indicating misalignment with gravitational forces.
- Droplet motion decorrelation (α) exhibits complex dependence on droplet size, contrasting with behavior in a dish.
Conclusions:
- The Marangoni effect significantly alters active droplet settling dynamics in confined geometries.
- A proposed relation describes the crossover radius for maximal decorrelation in active settling droplets.
- Findings highlight differences in active droplet behavior between capillary channels and open systems.
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