Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Drop in found out

07.11.2001


Long drop: soap and air keep water afloat on water.
© Y. Amarouchene


Air lets water droplets skim across the kitchen sink.

Scientists have found the answer to a question pondered over many a kitchen sink: why do little droplets skim across the surface of washing-up water rather than mix with it?

Yacine Amarouchene and colleagues at the University of Bordeaux in Talence, France have discovered that the height from which the drops fall has no effect on their lifespan1.



Soap, detergent - and indeed food grease - are ’surfactants’. They form a kind of skin on the surface of water that stabilizes a droplet, preventing it from merging where it rests. Droplets of pure water coalesce in a few thousandths of a second; when they contain a little surfactant they last hundreds of times longer.

The interest in coalescing droplets goes beyond the kitchen sink. When applying thin coats of a liquid as a spray, for example in car-painting, droplets need to merge quickly and smoothly at the surface of the wet film. Emulsions and foams, meanwhile, are sustained by inhibiting or slowing the coalescence of droplets or bubbles. Amarouchene’s group hope their theory might help chemical engineers and technologists to promote or prevent the effect, as required.

Droplets containing soap or detergent that fall a short distance onto a water surface bounce as if on a trampoline, the researchers found. The droplets then rest in a slight dip with a very thin film of air separating the two water surfaces.

How long the droplet lasts depends on how quickly the air is squeezed out from this interface, which in turn depends on the concentration of surfactants at the droplet surface. For pure water, the air film can thin very fast. A skin of surfactants at the water surface makes it harder for air to flow past. Air flow deforms this skin; and deformed skin slows the flow further.

The researchers find that, for a droplet of a particular size and containing a particular amount of surfactant, there is a characteristic residence time on the surface. Dropping them from increasing heights simply increases the chance of rupture on impact - it doesn’t alter the average lifetime of the drops that survive.

References
  1. Amarouchene, Y., Cristobal, G. & Kellay, H. Noncoalescing drops. Physical Review Letters, 87, 206104 (2001).


PHILIP BALL | © Nature News Service

More articles from Life Sciences:

nachricht Bolstering fat cells offers potential new leukemia treatment
17.10.2017 | McMaster University

nachricht Ocean atmosphere rife with microbes
17.10.2017 | King Abdullah University of Science & Technology (KAUST)

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Neutron star merger directly observed for the first time

University of Maryland researchers contribute to historic detection of gravitational waves and light created by event

On August 17, 2017, at 12:41:04 UTC, scientists made the first direct observation of a merger between two neutron stars--the dense, collapsed cores that remain...

Im Focus: Breaking: the first light from two neutron stars merging

Seven new papers describe the first-ever detection of light from a gravitational wave source. The event, caused by two neutron stars colliding and merging together, was dubbed GW170817 because it sent ripples through space-time that reached Earth on 2017 August 17. Around the world, hundreds of excited astronomers mobilized quickly and were able to observe the event using numerous telescopes, providing a wealth of new data.

Previous detections of gravitational waves have all involved the merger of two black holes, a feat that won the 2017 Nobel Prize in Physics earlier this month....

Im Focus: Smart sensors for efficient processes

Material defects in end products can quickly result in failures in many areas of industry, and have a massive impact on the safe use of their products. This is why, in the field of quality assurance, intelligent, nondestructive sensor systems play a key role. They allow testing components and parts in a rapid and cost-efficient manner without destroying the actual product or changing its surface. Experts from the Fraunhofer IZFP in Saarbrücken will be presenting two exhibits at the Blechexpo in Stuttgart from 7–10 November 2017 that allow fast, reliable, and automated characterization of materials and detection of defects (Hall 5, Booth 5306).

When quality testing uses time-consuming destructive test methods, it can result in enormous costs due to damaging or destroying the products. And given that...

Im Focus: Cold molecules on collision course

Using a new cooling technique MPQ scientists succeed at observing collisions in a dense beam of cold and slow dipolar molecules.

How do chemical reactions proceed at extremely low temperatures? The answer requires the investigation of molecular samples that are cold, dense, and slow at...

Im Focus: Shrinking the proton again!

Scientists from the Max Planck Institute of Quantum Optics, using high precision laser spectroscopy of atomic hydrogen, confirm the surprisingly small value of the proton radius determined from muonic hydrogen.

It was one of the breakthroughs of the year 2010: Laser spectroscopy of muonic hydrogen resulted in a value for the proton charge radius that was significantly...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

ASEAN Member States discuss the future role of renewable energy

17.10.2017 | Event News

World Health Summit 2017: International experts set the course for the future of Global Health

10.10.2017 | Event News

Climate Engineering Conference 2017 Opens in Berlin

10.10.2017 | Event News

 
Latest News

Ocean atmosphere rife with microbes

17.10.2017 | Life Sciences

Neutrons observe vitamin B6-dependent enzyme activity useful for drug development

17.10.2017 | Life Sciences

NASA finds newly formed tropical storm lan over open waters

17.10.2017 | Earth Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>