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Structure of circulation flows in polymer solution droplets receding on flat surfaces
Yu Yoshitake1, Shohei Yasumatsu, Masayuki Kaneda
1Department of Chemical Engineering, Graduate School of Engineering, Kyushu University, Motooka 744, Fukuoka 819-0395 Japan.
Langmuir : the ACS Journal of Surfaces and Colloids
|November 26, 2009
Summary
Internal flows in polymer solution droplets depend on solvent and concentration. Numerical models reveal that flow structures change with Marangoni numbers, explaining experimental observations of circulation direction.
Area of Science:
- Fluid dynamics
- Polymer science
- Surface science
Background:
- Previous experiments showed polymer solution droplet flow direction varied with solvent and concentration.
- Understanding the underlying fluid dynamics is crucial for predicting droplet behavior.
Purpose of the Study:
- To numerically investigate the internal flow dynamics in polymer solution droplets.
- To identify the reasons for the experimentally observed dependence of circulation flow direction on solvent and solute concentration.
Main Methods:
- Development and application of a mathematical model for droplet internal flow.
- Numerical simulations were performed to analyze flow patterns at varying Marangoni numbers.
- Calculated velocities were compared qualitatively with experimental data.
Main Results:
- A single circulation flow develops at low Marangoni numbers.
- Double circulation flows initiate after a single flow develops at high Marangoni numbers.
- Numerical predictions of velocity dependence on solvent and concentration align with experimental findings.
Conclusions:
- The change in flow structures, specifically single versus double circulation, explains the experimentally observed differences in flow direction.
- Marangoni number is a key parameter influencing internal flow patterns in receding droplets.
- Contact angle and droplet dimensions also impact transport phenomena.
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