What the study found
The study found that the final shape of spreading droplets of yield-stress fluids depends on both gravity and yield stress. In microgravity, the researchers could separate the effects of surface tension from those of yield stress.
Why the authors say this matters
The authors indicate that microgravity lets them vary two dimensionless numbers independently: the Bond number, which compares gravity to surface tension, and the plastocapillary number, which compares yield stress to surface tension. The study suggests this helps test scaling laws for viscoplastic fluids, meaning fluids that behave like solids until a threshold stress is exceeded.
What the researchers tested
The researchers performed droplet-spreading experiments both in a drop tower under microgravity and under normal terrestrial gravity. They deposited droplets onto a thin film of the same material to mimic a fully wetting surface and to test scaling laws derived from the thin-film equation for viscoplastic fluids.
What worked and what didn't
The experiments showed how final droplet shape changes with yield stress and gravity. Simulations using a viscoelastic model with shear-thinning agreed well with the observed droplet shapes, while possible deviations were discussed for cases with non-negligible elastic effects and large plastocapillary numbers.
What to keep in mind
The abstract notes possible deviations in regimes with notable elastic effects and large plastocapillary numbers, but it does not give detailed limitations beyond that. The summary also does not describe numerical values or specific shape changes beyond the general dependence on gravity and yield stress.
Key points
- The final shape of spreading droplets depends on both gravity and yield stress.
- Microgravity allowed the researchers to separate surface-tension effects from yield-stress effects.
- The experiments used droplets placed on a thin film of the same material to mimic a fully wetting surface.
- Simulations with a viscoelastic shear-thinning model agreed well with the observed droplet shapes.
- Possible deviations were discussed for large yield stress and non-negligible elastic effects.
Disclosure
- Research title:
- Gravity and surface tension both shape yield-stress droplet spreading
- Authors:
- Linnea Heitmeier, Olfa D’Angelo, Maziyar Jalaal, Thomas Voigtmann
- Institutions:
- Deutsches Zentrum für Luft- und Raumfahrt e. V. (DLR), Heinrich Heine University Düsseldorf, National Higher French Institute of Aeronautics and Space, Amsterdam University of Applied Sciences
- Publication date:
- 2026-04-21
- OpenAlex record:
- View
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