Asymmetric coalescence of two droplets with different surface tensions is caused by capillary waves

Michiel A. Hack*, Patrick Vondeling, Menno Cornelissen, Detlef Lohse, Jacco H. Snoeijer, Christian Diddens, Tim Segers

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

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Abstract

When two droplets with different surface tensions collide, the shape evolution of the merging droplets is asymmetric. Using experimental and numerical techniques, we reveal that this asymmetry is caused by asymmetric capillary waves, which are the result of the different surface tensions of the droplets. We show that the asymmetry is enhanced by increasing the surface tension difference, and suppressed by increasing the inertia of the colliding droplets. Furthermore, we study capillary waves in the limit of no collisional inertia. We reveal that the asymmetry is not directly caused by Marangoni forces. In fact, somehow counterintuitive, asymmetry is strongly reduced by the Marangoni effect. Rather, the different intrinsic capillary wave amplitudes and velocities associated with the different surface tensions of the droplets lie at the origin of the asymmetry during droplet coalescence.

Original languageEnglish
Article number104002
JournalPhysical review fluids
Volume6
Issue number10
DOIs
Publication statusPublished - Oct 2021

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