Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Spheres can form squares

Everybody who has tried to stack oranges in a box knows that a regular packing of spheres in a flat layer naturally leads to a hexagonal pattern, where each sphere is surrounded by six neighbours in a honeycomb-like fashion.

In an article just published on-line in PNAS, researchers from Wageningen University (Netherlands) report an exception to this rule: when small, micrometer-sized particles are placed on a curved oil-water surface, they arrange in a square pattern, as on a chessboard.

Since a number of decades, scientists are looking for strategies to create ordered crystal structures of regularly arranged small particles. Such crystals are interesting, because they can be used to control, modulate, or steer visible light in applications like lasers or other optical devices. While creating hexagonal patterns is relatively easy – this is the natural way in which the particles tend to order – anything different from that is much more difficult.

The team from the Laboratory of Physical Chemistry and Colloid Science at Wageningen University, part of Wageningen UR, has now found a way to create square particle arrays. To do this, they make use of the surface tension of the underlying oil-water surface, that is the tendency of the surface to minimize its area. When a particle sticks to the liquid surface it deforms the surface somewhat, and thereby increases the total area.

The surface tension acts to minimize these deformations, which can be done by clustering all the particles together. This effect is also responsible for the clumping of breakfast cereals in a bowl of milk or of bubbles at the surface of a soft drink. The researchers have found that this effective attraction between particles resulting from the surface tension depends on how the liquid surface is curved.

A slight curving of the surface already makes the interaction between particles highly dependent on their relative orientation, with attraction in two perpendicular directions and repulsion in the other directions. This is what causes the particles to arrange spontaneously in square patterns.

The researchers believe that their findings will lead to new bottom-up strategies for the design of structured materials, to be used in high-tech optical applications.

Capillarity-induced ordering of spherical colloids on an interface with anisotropic curvature.Dmitry Ershov, Joris Sprakel, Jeroen Appel, Martien A. Cohen Stuart, and Jasper van der Gucht. PNAS (early edition, May 2013). The research has been supported financially by the Netherlands Organisation for Scientific Research, NWO.
For more information please contact prof.dr Jasper van der Gucht, Head of the Laboratory of Physical Chemistry and Colloid Science, tel. + 31 317 483066, or Jac Niessen, science information officer, Wageningen UR, tel. + 31 317 485003,

Caption: Particle organization on oil-water interface of a droplet. The particles are labeled with a fluorescent marker to make them visible.

Wageningen University is part of Wageningen UR (University & Research centre).The mission of Wageningen UR is ‘To explore the potential of nature to improve the quality of life’. Within Wageningen UR, nine research institutes – both specialised and applied – have joined forces with Wageningen University to help answer the most important questions in the domain of healthy food and living environment. With approximately 30 locations (in the Netherlands, Brazil, Chile, Ethiopia and China), 6,000 members of staff and 9,000 students, Wageningen UR is one of the leading organisations in its domain worldwide. The integral approach to problems and the cooperation between the exact sciences and the technological and social disciplines are at the heart of the Wageningen Approach.

Jac Niessen | Wageningen University
Further information:

More articles from Life Sciences:

nachricht Don't Give the Slightest Chance to Toxic Elements in Medicinal Products
23.03.2018 | Physikalisch-Technische Bundesanstalt (PTB)

nachricht North and South Cooperation to Combat Tuberculosis
22.03.2018 | Universität Zürich

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Researchers Discover New Anti-Cancer Protein

An international team of researchers has discovered a new anti-cancer protein. The protein, called LHPP, prevents the uncontrolled proliferation of cancer cells in the liver. The researchers led by Prof. Michael N. Hall from the Biozentrum, University of Basel, report in “Nature” that LHPP can also serve as a biomarker for the diagnosis and prognosis of liver cancer.

The incidence of liver cancer, also known as hepatocellular carcinoma, is steadily increasing. In the last twenty years, the number of cases has almost doubled...

Im Focus: Researchers at Fraunhofer monitor re-entry of Chinese space station Tiangong-1

In just a few weeks from now, the Chinese space station Tiangong-1 will re-enter the Earth's atmosphere where it will to a large extent burn up. It is possible that some debris will reach the Earth's surface. Tiangong-1 is orbiting the Earth uncontrolled at a speed of approx. 29,000 km/h.Currently the prognosis relating to the time of impact currently lies within a window of several days. The scientists at Fraunhofer FHR have already been monitoring Tiangong-1 for a number of weeks with their TIRA system, one of the most powerful space observation radars in the world, with a view to supporting the German Space Situational Awareness Center and the ESA with their re-entry forecasts.

Following the loss of radio contact with Tiangong-1 in 2016 and due to the low orbital height, it is now inevitable that the Chinese space station will...

Im Focus: Alliance „OLED Licht Forum“ – Key partner for OLED lighting solutions

Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP, provider of research and development services for OLED lighting solutions, announces the founding of the “OLED Licht Forum” and presents latest OLED design and lighting solutions during light+building, from March 18th – 23rd, 2018 in Frankfurt a.M./Germany, at booth no. F91 in Hall 4.0.

They are united in their passion for OLED (organic light emitting diodes) lighting with all of its unique facets and application possibilities. Thus experts in...

Im Focus: Mars' oceans formed early, possibly aided by massive volcanic eruptions

Oceans formed before Tharsis and evolved together, shaping climate history of Mars

A new scenario seeking to explain how Mars' putative oceans came and went over the last 4 billion years implies that the oceans formed several hundred million...

Im Focus: Tiny implants for cells are functional in vivo

For the first time, an interdisciplinary team from the University of Basel has succeeded in integrating artificial organelles into the cells of live zebrafish embryos. This innovative approach using artificial organelles as cellular implants offers new potential in treating a range of diseases, as the authors report in an article published in Nature Communications.

In the cells of higher organisms, organelles such as the nucleus or mitochondria perform a range of complex functions necessary for life. In the networks of...

All Focus news of the innovation-report >>>



Industry & Economy
Event News

Virtual reality conference comes to Reutlingen

19.03.2018 | Event News

Ultrafast Wireless and Chip Design at the DATE Conference in Dresden

16.03.2018 | Event News

International Tinnitus Conference of the Tinnitus Research Initiative in Regensburg

13.03.2018 | Event News

Latest News

Modular safety concept increases flexibility in plant conversion

22.03.2018 | Trade Fair News

New interactive map shows climate change everywhere in world

22.03.2018 | Earth Sciences

New technologies and computing power to help strengthen population data

22.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>