Argonne Researchers Use Electric Field To Manipulate Tiny Particles

TECH SPACE

Toroidal vortices (t-vortices) attract each other and coalesce, resulting in large-scale dynamic condensates. The evolution of these condensates depends on the electric field direction.

Argonne - Mar 26, 2003
Intricate patterns formed by granular materials under the influence of electrostatic fields have scientists at the U.S. Department of Energy's Argonne National Laboratory dreaming of new ways to create smaller structures for nanotechnologies.

With a combination of electric fields and fluid mixtures, researchers Igor Aronson, Maksim Sapozhnikov, Yuri Tolmachev and Wai Kwok can cause tiny spheres of bronze and other metals to self-assemble into crystalline patterns, honeycombs, pulsating rings and bizarre two-lobed structures that whirl like tiny propellers.

Such self-assembling behavior could be exploited to create the next generation nanostructures or tiny micromechanical devices. Their work has been reported in the Physical Review Letters (Phys. Rev. Lett. 90, 114301, 2003).

The research started about four years ago, when Igor Aronson was studying the surprisingly regular patterns formed when granular materials like sand are vibrated, seeking clues to the dynamics of such substances.

"Despite about a thousand years of practical experience, we still don't completely understand granular materials," Aronson said. "They can display the properties of solids or liquids, and behaviors that defy conventional physics."

Aronson and colleagues investigated the reaction of a very fine granular material in an electrostatic field. They placed a quarter-teaspoon of 100-micron bronze spheres between two transparent sheets coated with conducting material.

Under high voltage, each bronze sphere acquires a charge from the bottom plate and is attracted to the upper sheet. The spheres reverse charge when they hit the upper sheet and are repelled back toward the lower sheet. As the process repeats 40 times per second, the bronze particles form a shimmering "gas" between the two plates.

Groups of particles, responding to the electric field from the plates and from each other, tend to cluster together and coalesce into large, random groups.

Maksim Sapozhnikov, a postdoctoral researcher working under Aronson's supervision, then filled the electrostatic cell with various non-conducting fluids, including toluene, octane and others. The results were essentially random until he tried phenotole, a colorless, oily fluid used in medicines and dyes.

Then came the surprise - at around 1,000 volts, the particles began to form regular patterns. By varying the voltage, the spacing between the plates and the amount of conductive fluid in the mix, the researchers found they could create a regularly spaced array of dots (crystals), honeycombs and other forms.

The results then were reproduced with other dielectric liquids mixed with small amount of ethanol to control the electrical conductivity of the solution.

"Particles interact with each other and create hydrodynamic forces in the liquid. These interactions create the patterns," Aronson said. "You can actually 'tune' the patterns by adding impurities to the liquid."

But the patterns aren't always static. The particles can form rings that grow, absorb other clusters of particles, then burst open. Sometimes madly spinning strange creatures are formed. "They grow, they rotate, they do all kinds of crazy things," Aronson said. "The rotation, especially, is still not understood. The physics are complex, and we only partially understand them."

The ability of some materials to organize themselves into repeating patterns is of special interest to nanotechnologists. Tiny clusters of particles - measured in billionths of a meter, or about 1/500th the width of a human hair - exhibit different properties than their larger bulk counterparts.

Argonne researchers have learned that they are more chemically reactive, exhibit new electronic properties and can be used to create materials that are stronger, tougher and more resistant to friction and wear than bulk materials.

Getting nanometer-sized particles to self-assemble into useful structures is one of the field's most difficult challenges. Self-assembly techniques are usually driven by thermodynamic forces, which dictate the type of complex pattern formation.

"This electrostatic method provides an additional way to control the self-assembly process," Aronson said. "It's another 'handle' we can use to manipulate the particles."

TECH SPACE

Jefferson Lab Takes Center Stage New SNS Accelerator

Oak Ridge - Jan 30, 2003
Thermos bottles usually don't weigh nearly five tons or measure almost 26 feet end-to-end. But these aren't run-of-the-mill containers for soup or coffee. Rather, they're the complex, state-of-the-art supercooled components in which particle beams are accelerated for scientific 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

The content herein, unless otherwise known to be public domain, are Copyright 1995-2016 - 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. 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. Privacy Statement All images and articles appearing on Space Media Network have been edited or digitally altered in some way. Any requests to remove copyright material will be acted upon in a timely and appropriate manner. Any attempt to extort money from Space Media Network will be ignored and reported to Australian Law Enforcement Agencies as a potential case of financial fraud involving the use of a telephonic carriage device or postal service.