. 24/7 Space News .
Understanding what's happening inside liquid droplets
by Staff Writers
Atlanta GA (SPX) Mar 09, 2017

A sheet laser illuminates a toroidal droplet formed in silicone oil to help researchers image the flow field movement inside the droplet. Image courtesy John Toon and Georgia Tech. For a larger version of this image please go here. Watch a video on the research here.

For most people, the drip, drip, drip of a leaking faucet would be an annoyance. But for Georgia Institute of Technology Ph.D. candidate Alexandros Fragkopoulos, what happens inside droplets is the stuff of serious science. In the laboratory of Alberto Fernandez-Nieves in Georgia Tech's School of Physics, Fragkopoulos is studying how toroidal droplets - which initially take the shape of a donut - evolve into spherical droplets by collapsing into themselves or breaking up into smaller droplets.

Work with droplets has implications for the life sciences, where biological materials, including cells, undergo shape changes reminiscent of droplet behavior. And the findings could improve industrial processes ranging from fuel injectors to chemical processes that depend on droplet formation. In the work, researchers in the Fernandez-Nieves lab have developed a new understanding of the processes that control the evolution of unstable, donut-shaped droplets, helping them clarify the complex interplay of forces relevant to the problem.

"Surface tension drives the evolution of the droplets," said Fragkopoulos. "Fluids tend to minimize their surface area for a given volume because that minimizes the energy required to have an interface between different fluids. Spherical shapes minimize that energy, and as a result, toroidal droplets want to evolve to become spherical. We're studying how that transition occurs."

Using a sheet of laser light to observe the scattering from polystyrene particles placed into droplets formed within thick silicone oil, the researchers have observed in detail how droplets change shape - and which factors set the droplets on the path to either collapse or breakup. The research, which was supported by the National Science Foundation, was reported March 1 in the journal Proceedings of the National Academy of Sciences.

"The viscous forcing as the torus collapses exerts stress on the interface, which causes it to both have a circulation inside the torus and deform its surface," said Fragkopoulos. "We need to take into account these stresses to completely understand the evolution of the droplets."

The impetus for the experimental work was inconsistencies between theoretical predictions and computer simulation of toroidal droplet transitions. What the Georgia Tech researchers found tends to back up the simulation results. "However, the earlier theoretical work was essential in guiding the theory efforts and in illustrating what the problem was in order to correctly describe the experimental results," said Fernandez-Nieves.

"Parameters such as the aspect ratio - the overall dimension of the torus divided by the dimensions of the tube - determine whether the toroidal droplet can break up, or if it will simply collapse into itself," said Fragkopoulos. "We found that the toroidal droplet deforms a lot from the donut shape as it collapses. It flattens as it develops, which was initially unexpected. We had expected the torus to be symmetrical and nicely circular, which is not what we found."

The breakup or collapse of ordinary raindrops is known to involve the formation of a donut-like rim. However, the process is rather uncontrolled and takes place quickly, so quickly that only high-speed cameras could see it. To allow detailed study of the transition and imaging the flow field within the drops, Fragkopoulos dramatically slowed down the evolution by creating droplets within a type of silicone oil that is six times more viscous than honey. Instead of ordinary water, he used distilled water into which polyethylene glycol has been mixed to further slow the dynamics.

The water is introduced into a rotating bath of the silicone oil using a tiny needle injector. By controlling the pumping rate and where the needle inserts the water, the researchers can control the geometrical parameters of the toroidal droplets, specifically the thickness of the ring and the relative size of the hole inside it. The droplets they study range in size up to about a centimeter in diameter. "This simple strategy affords exquisite control," said Fernandez-Nieves.

Polystyrene beads in the water allow the researchers to use particle image velocimetry (PIV) to see the flow fields within the droplets, showing how the cross section deviates from circular over time.

"We are using the difference in viscosity to generate the torus," Fragkopoulos explained. "We are using viscous forces to generate the droplets, because it's important to slow down the dynamics of the torus collapse so we can have enough time and resolution to see the flow fields developing inside it."

Research into droplet formation has tended to be applications-focused. Now Fragkopoulos and Fernandez-Nieves are using their experimental and theoretical work to address other science problems.

"We are now using the methods for creating toroidal objects made from different materials to study problems in condensed matter and bioengineering," said Fernandez-Nieves. "We started working on toroidal droplets with the idea of studying how topology and geometry affected how ordered materials are affected by these aspects, and later to address how curvature affects cell behavior. We wanted to make nontrivial geometries so we could study how this affects behavior," added Fragkopoulos.

The next step in the work is to study electrically-charged droplets, which are widely used industrially. The electrical charges add a new wrinkle to the flow fields and change how the toroidal droplets transform. In addition to those already mentioned, the research included former graduate and undergraduate students in the Fernandez-Nieves lab, Ekapop Pairam and Eric Berger, and Prof. Phil Segre at Oxford College, Georgia.

Alexandros A. Fragkopoulos, et al., "The shrinking instability of toroidal droplets," (Proceedings of the National Academy of Sciences, 2017).

Coffee-ring effect leads to crystallization control
Thuwal, Saudi Arabia (SPX) Mar 07, 2017
A chance observation of crystals forming a mark that resembled the stain of a coffee cup left on a table has led to the growth of customized polycrystals with implications for faster and more versatile semiconductors. Thin-film semiconductors are the foundation of a vast array of electronic and optoelectronic devices. They are generally fabricated by crystallization processes that yield polycrys ... read more

Related Links
Georgia Institute of Technology
Space Technology News - Applications and Research

Thanks for being here;
We need your help. The SpaceDaily news network continues to grow but revenues have never been harder to maintain.

With the rise of Ad Blockers, and Facebook - our traditional revenue sources via quality network advertising continues to decline. And unlike so many other news sites, we don't have a paywall - with those annoying usernames and passwords.

Our news coverage takes time and effort to publish 365 days a year.

If you find our news sites informative and useful then please consider becoming a regular supporter or for now make a one off contribution.
SpaceDaily Contributor
$5 Billed Once

credit card or paypal
SpaceDaily Monthly Supporter
$5 Billed Monthly

paypal only

Comment on this article using your Disqus, Facebook, Google or Twitter login.

Share this article via these popular social media networks
del.icio.usdel.icio.us DiggDigg RedditReddit GoogleGoogle

Orion spacecraft achieves key safety milestone

The NASA Imager Dentists Use Daily

Marshall shakes, packs, ships and tracks NASA payloads

NASA and SpaceX gives ASU a competitive edge in technological innovation

SpaceX says it will fly civilians to the moon next year

Moon tourists risk rough ride, experts say

Flight Hardware for NASA's Space Launch System on Its Way to Cape

Spacex To Send Privately Crewed Dragon Spacecraft Beyond The Moon Next Year

NASA Orbiter Steers Clear of Mars Moon Phobos

Remnants of a mega-flood on Mars

Science checkout continues for ExoMars orbiter

NASA Explores Opportunity for Smaller Experiments to 'Hitch a Ride' to Mars

Thinking Big: China Hopes to Conduct 2nd Mission to Mars by 2030

China to Conduct Test Flight of CZ-8 Carrier Rocket by 2018

China to launch first high-throughput communications satellite in April

Chinese cargo spacecraft set for liftoff in April

OneWeb, Intelsat merge to advance satellite internet

GomSpace to supply satellites for Sky and Space Global constellation

Kacific places order with Boeing for a high throughput satellite

ESA affirms Open Access policy for images, videos and data

Coffee-ring effect leads to crystallization control

3-D printing with plants

Researchers remotely control sequence in which 2-D sheets fold into 3-D structures

Scientists demonstrate improved particle warning to protect astronauts

Faraway Planet Systems Are Shaped Like the Solar System

Biochemical 'fossil' shows how life may have emerged without phosphate

The missing link in how planets form

Volcanic hydrogen spurs chances of finding exoplanet life

Juno to remain in current orbit at Jupiter

Europa Flyby Mission Moves into Design Phase

NASA receives science report on Europa lander concept

New Horizons Refines Course for Next Flyby

The content herein, unless otherwise known to be public domain, are Copyright 1995-2024 - Space Media Network. All websites are published in Australia and are solely subject to Australian law and governed by Fair Use principals for news reporting and research purposes. AFP, UPI and IANS news wire stories are copyright Agence France-Presse, United Press International and Indo-Asia News Service. ESA news reports are copyright European Space Agency. All NASA sourced material is public domain. Additional copyrights may apply in whole or part to other bona fide parties. All articles labeled "by Staff Writers" include reports supplied to Space Media Network by industry news wires, PR agencies, corporate press officers and the like. Such articles are individually curated and edited by Space Media Network staff on the basis of the report's information value to our industry and professional readership. Advertising does not imply endorsement, agreement or approval of any opinions, statements or information provided by Space Media Network on any Web page published or hosted by Space Media Network. General Data Protection Regulation (GDPR) Statement Our advertisers use various cookies and the like to deliver the best ad banner available at one time. All network advertising suppliers have GDPR policies (Legitimate Interest) that conform with EU regulations for data collection. By using our websites you consent to cookie based advertising. If you do not agree with this then you must stop using the websites from May 25, 2018. Privacy Statement. Additional information can be found here at About Us.