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Induction of Microstreaming by Nonspherical Bubble Oscillations in an Acoustic Levitation System
Published on: May 9, 2021
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Evaporation Caused Invaginations of Acoustically Levitated Colloidal Droplets
Hongyue Chen1, Yongjian Zhang2, Heyi Wang2
1MOE Key Laboratory of Material Physics and Chemistry under Extraordinary Conditions, School of Physical Science and Technology, Northwestern Polytechnical University, Xi'an 710129, China.
Nanomaterials (Basel, Switzerland)
|January 8, 2023
Summary
Acoustic levitation of colloidal droplets causes surface invagination during evaporation. Droplet concentration dictates whether a bowl- or doughnut-like structure forms due to uneven shell thickness and acoustic radiation pressure.
Area of Science:
- Materials Science
- Fluid Dynamics
- Acoustics
Background:
- Controlled buckling of colloidal droplets is crucial for applications in pharmaceuticals, coatings, and material self-assembly.
- Acoustic levitation offers a method for manipulating and studying droplet behavior without physical contact.
Purpose of the Study:
- To investigate the evaporation process of polytetrafluoroethylene (PTFE) colloidal droplets under acoustic levitation.
- To characterize the resulting structural changes, specifically surface invagination, as a function of particle concentration.
Main Methods:
- Acoustic levitation was employed to levitate PTFE colloidal droplets.
- Droplets with two distinct particle concentrations (60 wt% and 20 wt%) were subjected to controlled evaporation.
- The morphological changes, including surface invagination, were observed and analyzed.
Main Results:
- Evaporation induced surface invagination in acoustically levitated PTFE droplets.
- High concentration droplets (60 wt%) formed bowl-shaped structures due to upper surface invagination.
- Low concentration droplets (20 wt%) exhibited invagination on both upper and lower surfaces, creating doughnut-like structures.
Conclusions:
- The concentration-dependent structural changes are attributed to non-uniform shell thickness caused by differential dispersant loss at the droplet equator and poles.
- Acoustic radiation pressure within the invagination further promotes buckling, influencing the final morphology.
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