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Critical angle for electrically driven coalescence of two conical droplets
James C Bird1, William D Ristenpart, Andrew Belmonte
1School of Engineering and Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA. jbird@fas.harvard.edu
Physical Review Letters
|November 13, 2009
Summary
Oppositely charged liquid drops either merge or separate after contact. This study reveals that the outcome depends on the cone angle formed by the drops, with a critical angle of 30.8 degrees determining the transition.
Area of Science:
- Fluid Dynamics
- Electrostatics
- Surface Science
Background:
- Oppositely charged liquid drops attract due to electrostatic forces.
- Close proximity of charged drops leads to deformation of their surfaces into conical shapes.
Purpose of the Study:
- To investigate the coalescence behavior of charged liquid drops upon contact.
- To determine the factors influencing immediate coalescence versus recoil.
- To develop a model predicting the transition between these behaviors.
Main Methods:
- Utilizing high-speed imaging to observe drop interactions.
- Controlling the cone angle by adjusting drop size and applied voltage.
- Developing a surface energy model based on volume-constrained area minimization.
Main Results:
- Coalescence occurs when the liquid cone slopes are small.
- Recoil is observed when the cone slopes exceed a critical value.
- The critical cone angle for the transition was measured to be approximately 30.8 degrees.
Conclusions:
- The coalescence of charged liquid drops is governed by the geometry of the deformed cones.
- A surface energy model accurately predicts the critical cone angle for the transition from coalescence to recoil.
- This finding provides insight into liquid behavior under electrical stress.
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