Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:


Less is more: Study of tiny droplets could have big applications

Under a microscope, a tiny droplet slides between two fine hairs like a roller coaster on a set of rails until — poof — it suddenly spreads along them, a droplet no more.
That instant of change, like the popping of soap bubble, comes so suddenly that it seems almost magical. But describing it, and mapping out how droplets stretch into tiny columns, is a key to understanding how liquids affect fibrous materials from air filters to human hair. And that knowledge allows scientists to better describe why water soaks into some materials, beads atop others and leaves others matted and clumped.

To get those answers, an international team of researchers led by scientists at Princeton University made a series of close observations of how liquid spreads along flexible fibers. They were able to construct a set of rules that govern the spreading behavior, including some unexpected results. In a paper published Feb. 23 in Nature, the researchers found that a key parameter was the size of the liquid drop.

"That surprised us," said Camille Duprat, the paper's lead author. "No one had thought about volume very much before."

Duprat, a postdoctoral researcher in the Department of Mechanical and Aerospace Engineering, said the research team was able to determine drop sizes that maximized wetting along certain fibers, which could allow for increased efficiency in industrial applications of liquids interacting with fibrous materials — from cleaning oil slicks to developing microscopic electronics. The team also discovered a critical drop size above which the drop would not spread along the fibers, but would remain perched like a stranded roller coaster car.

"If in any engineering problem you can learn an optimal size above which something does not happen, you have learned something very important about the system," said Howard Stone, a co-author of the paper.

A study led by researchers at Princeton University has yielded insights into how liquid spreads along flexible fibers, which could allow for increased efficiency in various industrial applications. The team's experiments show that the size of oil droplets determines whether they spread along flexible glass fibers. At the critical size (top two examples), the droplets expand into columns of liquid, but larger droplets sit immobile between the glass rods (bottom example). (Image courtesy of Camille Duprat and Suzie Protière)

Stone, the Donald R. Dixon '69 and Elizabeth W. Dixon Professor in Mechanical and Aerospace Engineering, said the team conducted a series of experiments observing how liquid spread along different types of fibers. The plan was to make broad observations and derive a governing theory from the experiments.

"We had a lot of results and at some point we started having these meetings trying to understand what we had," he said. "We realized the way to think about it was in the way of critical sizes."

Besides Duprat and Stone, the researchers included Alexander Beebe, a Princeton junior majoring in mechanical and aerospace engineering, and Suzie Protière, an associate scientist at the University of Pierre and Marie Curie in Paris. The research at Princeton was conducted with support from Unilever.

The researchers determined that the critical parameters governing how drops interact with flexible fibers were the size of the droplet, the flexibility and radii of the fibers, and the geometry of the fiber array (such as the space and angle between pairs of fibers).

The experiment examined the behavior of a droplet placed on a pair of flexible glass fibers that was clamped at one end and free at the other. When the drop was placed at the clamped end of the pair, the fibers bent inward and the drop moved toward the free end. As the drop moved further out, the fibers bent more, and the drop accelerated and elongated. At some point, the drop spontaneously spread and formed a liquid column between the now-coalesced fibers.

To understand the critical drop size at which no spreading occurred, the researchers measured the distance between the fibers at the instant that the spreading began. They concluded that spreading occurs when the spacing between the fibers dictates that it takes less energy for the liquid to form a column than it does to remain as a drop. The researchers were also able to use their observations to calculate an optimal drop size that resulted in a maximum spread of liquid along the fibers.

The researchers said their findings could have a wide array of applications. Waterfowls' feathers, for example, are a natural array of fibers that keep the birds warm and dry. When oil coats the feathers, it disrupts the fiber arrangement by clumping the feathers. Using goose feathers, the team found that oil droplets above a certain size did not spread along the fibers and allowed the feather to be cleaned more easily. Duprat said the findings could have implications for methods used to rescue injured birds and also for dispersants applied to oil slicks after accidents.

On the other hand, items such as aerosol-removal filters or hairsprays require total spreading along fibers for effectiveness. The control of droplet sizes could also prove important for the fabrication of microstructures by resulting in the optimal spread of liquid material along pillars and similar forms, such as those found in various forms of lithography used in micro- and nanofabrication.

"Materials react differently to different drop sizes," Duprat said. "You can design a material to react to a specific drop size or you can produce a drop size to affect a specific material."

John Sullivan | EurekAlert!
Further information:

More articles from Materials Sciences:

nachricht Custom sequences for polymers using visible light
22.03.2018 | Tokyo Metropolitan University

nachricht The search for dark matter widens
21.03.2018 | American Institute of Physics

All articles from Materials 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

Custom sequences for polymers using visible light

22.03.2018 | Materials Sciences

Scientists develop tiny tooth-mounted sensors that can track what you eat

22.03.2018 | Health and Medicine

Mat baits, hooks and destroys pollutants in water

22.03.2018 | Earth Sciences

Science & Research
Overview of more VideoLinks >>>