# Marangoni Motion (DD-024)

> When surface tension varies across a liquid, the stronger-pulling (higher-tension) region drags the surface toward itself. Fluid then streams from low surface tension to high. This is the Marangoni effect, named after Carlo Marangoni, who published on it in 1865. James Thomson first explained it in 1855 using 'tears of wine'. It's why a drop of soap or alcohol makes water rush away, why wine climbs the glass, and why sulfur traces change the shape of a weld pool. Chip makers use it to dry silicon wafers without spots.

- Department: Science (also Tech)
- First published: 2026-04-11
- Last updated: 2026-04-11
- Permalink: https://detailenjoyer.com/case/marangoni-motion/
- Author: Marcus Easterling (DetailEnjoyer), The Detail Department

## On the timeline

- **1855**: James Thomson explains the 'tears of wine'
- **1865**: Carlo Marangoni publishes his doctoral study of the effect
- **1870s**: J. Willard Gibbs gives the full theory
- **2015**: A study finds evaporative cooling also drives wine tears

Full timeline: https://detailenjoyer.com/timeline/?case=marangoni-motion

## Quick facts

- **DD-024-F01**: In the Marangoni effect, liquid flows from regions of low surface tension toward regions of high surface tension. It's why wine forms 'tears' on the glass. _(Write-up · Exhibit A (Flow along a surface-tension gradient))_
- **DD-024-F02**: Traces of sulfur or oxygen can reverse the Marangoni flow in a weld pool, turning a wide, shallow weld into a narrow, deep one. _(Write-up · Exhibit E (Shaping welds))_

## Write-up

Surface tension can make liquid pull itself across a surface. The Marangoni effect: fluid flows toward higher surface tension.

1. **Flow along a surface-tension gradient**: The Marangoni effect is mass transfer along an interface driven by a gradient in surface tension. Higher-tension liquid pulls harder on its surroundings, so the surface and the fluid under it flow from low tension toward high.
2. **Two ways to make the gradient**: The gradient can come from composition (soap, alcohol, surfactants) or from temperature, because surface tension usually falls as a liquid warms. Temperature-driven flow is called thermocapillary or Bénard–Marangoni convection.
3. **Tears of wine**: Alcohol evaporates from the thin film of wine on the glass, leaving it watery, with higher surface tension. That film pulls wine up the glass until its own weight brings it back down as 'tears'. A 2015 study found that evaporative cooling contributes too.
4. **Who found it**: James Thomson, Lord Kelvin's brother, identified the cause of wine tears in 1855. Carlo Marangoni published his doctoral study of the effect in 1865, and J. Willard Gibbs gave the full theory in the 1870s.
5. **Shaping welds**: In a weld pool, Marangoni forces usually push molten metal outward from the hot center, giving a wide, shallow pool. Traces of sulfur or oxygen can reverse the flow inward, making the pool narrow and deep.
6. **Coatings and printing**: Paint defects like craters, fisheyes and crawling are caused by flows driven by surface-tension differences. Engineers use Marangoni flows on purpose to cancel the 'coffee ring' that makes drying drops deposit at their edges.
7. **Drying microchips**: After wet processing, chip makers blow alcohol vapor over silicon wafers. The resulting Marangoni flow pulls the water off, leaving the wafer dry and spot-free.

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## Reel vs. record

- **Confirmed from the frames**: the Reel is about the Marangoni effect (caption at 0.9–2.4 s: 'The Marangoni effect is a physical phenomenon'). The direction, low to high surface tension, is correct. [Wikipedia; coatings chapter; COMSOL paper]
- **Imprecise**: 'because liquids naturally try to minimize surface energy'. The driving force is the surface-tension gradient itself, because higher-tension regions pull harder on the interface. Minimizing surface energy is the general principle behind surface tension, not the specific cause of the flow. [Wikipedia; Scientific Reports 2015]
- **Nuance**: welding and coating are well documented. 'Bubble formation' and 'biological systems' are vaguer: Marangoni stresses stabilize soap films and foams, and they are studied in surfactant spreading. The Reel gives no specific example. [Wikipedia; Langmuir 2018]

## Video: Marangoni Motion: Surface Tension Can Make Liquid Pull Itself Across a Surface

- Duration: 21.2 s · Published: 2026-04-11
- File: https://detailenjoyer.com/assets/videos/DW_0WhlEXLj.mp4

### Transcript

DID YOU KNOW? The Marangoni effect is a physical phenomenon where fluid flows from areas of low surface tension to areas of high surface tension. This movement happens because liquids naturally try to minimize surface energy, causing the fluid to pull itself along the surface. The Marangoni effect plays an important role in processes like welding, coating, bubble formation, and even biological systems. NOW YOU KNOW!

## Questions & answers

**Q: In the Marangoni effect, which way does liquid flow?**  
A: Higher-tension regions pull harder, so fluid flows from low toward high surface tension. _(Source: Write-up · Exhibit A (Flow along a surface-tension gradient) · Marangoni effect (Wikipedia); Numerical Analysis of Effect of Surface Active Elements on Marangoni Convection (COMSOL conference paper); Surface Defects: Causes, Prevention, and Remedies (coatings handbook chapter, Wiley))_

**Q: Which everyday sight is a classic example of the Marangoni effect?**  
A: Alcohol evaporating from the film raises its surface tension and pulls wine up the glass. _(Source: Write-up · Exhibit C (Tears of wine) · Tears of wine: new insights on an old phenomenon (Scientific Reports, 2015); Marangoni effect (Wikipedia))_

**Q: Besides composition, what else can create a surface-tension gradient?**  
A: Surface tension usually drops as temperature rises, creating thermocapillary flow. _(Source: Write-up · Exhibit B (Two ways to make the gradient) · Marangoni effect (Wikipedia); Tears of wine: new insights on an old phenomenon (Scientific Reports, 2015))_

**Q: Who is the Marangoni effect named after?**  
A: Italian physicist Carlo Marangoni published his study in 1865; James Thomson described wine tears first, in 1855. _(Source: Write-up · Exhibit D (Who found it) · Marangoni effect (Wikipedia); Tears of wine: new insights on an old phenomenon (Scientific Reports, 2015))_

**Q: What can traces of sulfur or oxygen do to a weld pool?**  
A: They flip the temperature dependence of surface tension, reversing the flow inward. _(Source: Write-up · Exhibit E (Shaping welds) · Material Flow Behavior on Weld Pool Surface in Plasma Arc Welding (Applied Sciences, MDPI, 2020); Numerical Analysis of Effect of Surface Active Elements on Marangoni Convection (COMSOL conference paper))_

## Sources

- [Marangoni effect (Wikipedia)](https://en.wikipedia.org/wiki/Marangoni_effect)
- [Tears of wine: new insights on an old phenomenon (Scientific Reports, 2015)](https://www.nature.com/articles/srep16162)
- [Material Flow Behavior on Weld Pool Surface in Plasma Arc Welding (Applied Sciences, MDPI, 2020)](https://www.mdpi.com/2076-3417/10/10/3569)
- [Numerical Analysis of Effect of Surface Active Elements on Marangoni Convection (COMSOL conference paper)](https://www.comsol.com/paper/download/368741/mishra_paper.pdf)
- [Surface Defects: Causes, Prevention, and Remedies (coatings handbook chapter, Wiley)](https://doi.org/10.1002/9781394207305.ch16)
- [Dynamic Control of Particle Deposition in Evaporating Droplets (Langmuir, 2018; PMC)](https://pmc.ncbi.nlm.nih.gov/articles/PMC5797983/)

## Cite this case file

Easterling, Marcus. "Marangoni Motion." The Detail Department (DetailEnjoyer), case file DD-024, last updated Apr 11, 2026. https://detailenjoyer.com/case/marangoni-motion/