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 Nesting aids make agricultural fields attractive for bees
20.07.2017 | Julius-Maximilians-Universität Würzburg

nachricht The Kitchen Sponge – Breeding Ground for Germs
20.07.2017 | Hochschule Furtwangen

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Manipulating Electron Spins Without Loss of Information

Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.

For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...

Im Focus: The proton precisely weighted

What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.

To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...

Im Focus: On the way to a biological alternative

A bacterial enzyme enables reactions that open up alternatives to key industrial chemical processes

The research team of Prof. Dr. Oliver Einsle at the University of Freiburg's Institute of Biochemistry has long been exploring the functioning of nitrogenase....

Im Focus: The 1 trillion tonne iceberg

Larsen C Ice Shelf rift finally breaks through

A one trillion tonne iceberg - one of the biggest ever recorded -- has calved away from the Larsen C Ice Shelf in Antarctica, after a rift in the ice,...

Im Focus: Laser-cooled ions contribute to better understanding of friction

Physics supports biology: Researchers from PTB have developed a model system to investigate friction phenomena with atomic precision

Friction: what you want from car brakes, otherwise rather a nuisance. In any case, it is useful to know as precisely as possible how friction phenomena arise –...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

»We are bringing Additive Manufacturing to SMEs«

19.07.2017 | Event News

The technology with a feel for feelings

12.07.2017 | Event News

Leipzig HTP-Forum discusses "hydrothermal processes" as a key technology for a biobased economy

12.07.2017 | Event News

 
Latest News

Researchers create new technique for manipulating polarization of terahertz radiation

20.07.2017 | Information Technology

High-tech sensing illuminates concrete stress testing

20.07.2017 | Materials Sciences

First direct observation and measurement of ultra-fast moving vortices in superconductors

20.07.2017 | Physics and Astronomy

VideoLinks
B2B-VideoLinks
More VideoLinks >>>