Georgia Tech Research Horizons
Fall 2002
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Imitating Nature
Self-assembly technique may build designer polymers from modular scaffolds and building blocks.

Future designer polymers may be assembled like children's Lego toys using modular polymer scaffolds programmed to attract building blocks of small molecules. Weak and easily reversed chemical interactions would self-assemble those molecules to form complex structures with predictable physical and chemical properties.
image courtesy of Marcus Weck

This figure shows a comparison of the strategies to obtain copolymers: (A) traditional "living" polymerization strategy and (B) the self-assembly strategy. Conventional strategy (A) relies on the living polymerization of monomers, while the self-assembly method is based on a universal backbone and the controlled self-assembly of side-chains onto the backbone. Click here to enlarge image

In the natural world, self-assembly techniques produce thousands of varied life forms – from bacteria to human beings – based on a relatively small set of amino acids and nucleosides combined in different ways. By emulating this natural system, polymer chemists at the Georgia Institute of Technology hope to simplify the synthesis of new materials for light-emitting diodes, optical storage materials, biosensors, drug-delivery materials and other applications.

Already, the researchers have built copolymers that use independent chemical bonding mechanisms – also copied from the biological world – to simultaneously self-assemble two building-block functional groups through a simple "one-beaker" process.

"The goal is to simplify the synthesis of designer polymers via self-assembly using combinatorial chemistry," says Marcus Weck, an assistant professor in the Georgia Institute of Technology's School of Chemistry and Biochemistry. "Our group is taking design lessons from nature by incorporating into one system several of these weak interactions to get a degree of complexity that is difficult to achieve otherwise. We believe we now have the basic proof of principle to show that we will be able to address this problem."

He explained the concept and described research progress at the 224th national meeting of the American Chemical Society in Boston in August 2002.

"We are developing a system based on a polymer that contains two or three different basic units, each having a different recognition motive for weak interactions," Weck explains. "We would ultimately want to have a shelf with 30 or 40 polymer backbones. When someone needed a new LED, for instance, we would just take our polymer backbones, synthesize small molecules, then self-assemble them onto the polymer backbones. In one simple step in a beaker on the lab bench, we could assemble the polymer instead of taking two or three months to synthesize it with traditional methods."

– John Toon

For the text of the complete news release, see www.gtresearchnews.gatech.edu/newsrelease/MODULAR.htm.   For more information, contact Marcus Weck, School of Chemistry and Biochemistry, Georgia Tech, Atlanta, GA 30332-0400. (Telephone: 404-385-1796) (E-mail: marcus.weck@chemistry.gatech.edu).


Turn on the "Nanolight"
Nanometer-scale light source is first to show single-molecule electroluminescence.

Using photon emissions from individual molecules of silver, researchers at the Georgia Institute of Technology have created what may be the world's smallest electroluminescent light source.
© Proceedings of the National Academy of Sciences

Shown here is a (A) discolored silver oxide region between copper electrodes on a glass substrate in a vacuum, DC potentials of 9 volts were applied across the film; (B) multi-colored electroluminescence from single silver molecules occurs within the electrically discolored region. (C) These features exhibit dipole emission patterns and blinking dynamics (not shown) characteristics of single-molecule behavior.

Believed to be the first demonstration of electroluminescence from individual molecules, the work could lead to new types of nanometer-scale optical interconnects, high-resolution optical microscopy, nanometer-scale lithography and other applications that require very small light sources. And because single molecules are known to emit one photon at a time, the technique ultimately could be the basis for high-efficiency, quantum information processing and cryptography.

Though the effect was first reported in silver clusters composed of two to eight atoms, the researchers also demonstrated electroluminescence in similarly prepared copper clusters, suggesting the effect may broadly apply to other metals. Details of the research were reported in the Aug. 6, 2002 issue of the Proceedings of the National Academy of Sciences.

"This is the first time that anyone has seen electroluminescence from individual molecules," says Robert Dickson, an assistant professor in Georgia Tech's School of Chemistry and Biochemistry. "What we have observed involves sub-nanometer-scale sources to which an electric field is applied. These molecules emit very strongly, and are very robust."

Dickson and collaborators Tae-Hee Lee and Jose Gonzalez began with thin films of silver oxide that are not electroluminescent. By exposing the film to electrical current of about one amp, they "activated" some of the silver oxide molecules, which then appeared within "discolored" regions in the film. When electrodes were attached to the film and an alternating current applied, a thin line of silver clusters began to emit light in colors that varied depending on the size of the clusters. The system operated at room temperature.

"When you zoom in more closely, you can see the emissions coming from single molecules," Dickson says. "They blink and have dipole emission patterns. You see an incredibly thin line of emissive species close to the middle of the sample."

Electroluminescence occurs when an electron recombines with a positively charged molecule from which a single electron has been removed to create an electron-hole pair. First, an electron is removed from a molecule, creating a positive charge. Then, an electron is quickly injected into a different state of the same molecule. Because of the charge differences, the electron is attracted to the hole, and when they recombine, a photon is released.

– John Toon

For the complete news release, visit www.gtresearchnews.gatech.edu/newsrelease/NANOLIGHT.htm.   For more information, contact Robert Dickson, School of Chemistry and Biochemistry, Georgia Tech, Atlanta, GA 30332-0400. (Telephone: 404-894-4007) (E-mail: robert.dickson@chemistry.gatech.edu).


Dirty Air, Warmer Climate
Report assessing impact of soot on global warming could shift burden to developing nations and create new uncertainty in climate model predictions.

A new study on the role that atmospheric soot particles may play in global warming suggests a new near-term control strategy, introduces a new element of uncertainty in climate models and shifts more responsibility for curbing pollution to developing nations such as China and India.
© Science Magazine

A typical hazy day near Lin An, China. Black carbon emanates from a small brick factory.

Published in the Sept. 27, 2002, issue of the journal Science, the report – by researchers from NASA's Goddard Institute for Space Studies – suggests that by absorbing sunlight and altering weather patterns, light absorbing carbon-based particles could have nearly as much impact on global warming as carbon dioxide: a greenhouse gas that has long been considered the primary culprit in global warming. The soot particles are produced by diesel engines, cooking fires and other sources.

In a perspectives article published with the NASA Goddard paper, atmospheric researchers at the Georgia Institute of Technology describe some of the policy implications of the new findings. Among them:

"The study reported in Science really raises some important policy issues regarding soot," says Michael Bergin, an assistant professor in Georgia Tech's School of Earth and Atmospheric Sciences and co-author of the perspectives article. "In the past, researchers have felt that soot didn't really have a significant warming effect. But as we've learned more about the amount of black carbon emitted by countries like China and India, it appears now that soot could have important climatic effects, and that these effects may be almost as much as those of carbon dioxide."

In their perspectives article, Bergin and Professor William Chameides, also in Georgia Tech's School of Earth and Atmospheric Sciences, point out the differences between black carbon soot and greenhouse gases such as carbon dioxide and methane. For instance, soot particles are removed from the atmosphere on time scales of weeks to months, while carbon dioxide lingers for hundreds of years. That could point toward a better near-term control strategy.

"This could be 'low-hanging fruit' in trying to deal with the anthropogenic (human-caused) effects on the climate," Bergin notes. "From a policy standpoint, the payoff for controlling soot could be on the scale of years rather than centuries."

– John Toon

For the complete news release, see www.gtresearchnews.gatech.edu/newsrelease/SOOT.htm.   For more information, contact Michael Bergin, School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA 30332-0355. (Telephone: 404-894-9723) (E-mail: mike.bergin@ce.gatech.edu).


Measuring Atmospheric Pollutants
Instrument automates sampling of aerosols, provides more detailed data.

Scientists studying a class of atmospheric pollutants known as aerosols now have a new tool at their disposal – an instrument that automates the collection of air samples for analysis with sensitive ion chromatography equipment. Fine-particulate aerosol pollutants have attracted considerable attention because of recent studies linking them to human health effects such as heart attacks and respiratory problems.
photo by Gary Meek

Rodney Weber and Amy Sullivan check measurements being made by a Particle-in-Liquid-Sampler (lower left) connected to an ion chromatograph.

By automating the collection of data, the Particle-Into-Liquid-Sampler (PILS) developed at the Georgia Institute of Technology can measure particulate pollutants several times an hour, giving atmospheric scientists detailed time-dependent information not previously available. In a recent study, this ability to make frequent measurements revealed previously unknown morning and afternoon peaks in the levels of two key pollutants.

"Chemists have made significant advances in measuring trace species," says Rodney Weber, an assistant professor in Georgia Tech's School of Earth and Atmospheric Sciences. "We are applying those technologies to measure the composition of atmospheric particles. In combination with the ion chromatograph, this instrument provides some unique insights that could not be obtained before."

Weber presented information about the instrument's capabilities at the 224th national meeting of the American Chemical Society in August 2002 in Boston. The instrument is already in use around the world in studies conducted from aircraft, ships and ground stations.

Developed by Weber and colleague Douglas Orsini with help from Brookhaven National Laboratory, the PILS system uses small quantities of steam to form water droplets on individual aerosol particles. The water droplets containing the dissolved aerosols can then be captured and analyzed by ion chromatography techniques to detect as many as 15 different chemical species. The instrument can operate unattended for extended periods of time on the ground or in research aircraft, and can take samples as often as every four minutes

Scientists analyzing airborne particulates had previously relied on filters that collected the aerosol particles over a long period of time, usually 24 hours. The particles were then removed from the filters and dissolved in water for ion chromatograph analysis. It is these types of long time-intergrated measurements that have provided the air quality data to study the effects of aerosols on human health and that are the basis for current EPA particulate matter standards. This, however, is likely to change since the EPA is now moving toward more real-time measurements for assessing air quality.

– John Toon

For the full-text news release version of this article, see www.gtresearchnews.gatech.edu/ newsrelease/PILS.htm.   For more information, contact Rodney Weber, School of Earth and Atmospheric Sciences, Georgia Tech, Atlanta, GA 30332-0340. (Telephone: 404-894-1750) (E-mail: rodney.weber@eas.gatech.edu).


Faculty Awards and Honors
Georgia Tech faculty and staff receive recognition.

The American Association of Engineering Societies honored
Reginald DesRoches
Georgia Tech President Wayne Clough with the National Engineering Award, the organization's highest honor. Clough was recognized for his outstanding contributions as an educator, university administrator and statesman for the engineering profession.

Assistant Professor Reginald DesRoches of the School of Civil and Environmental Engineering and Associate Professor Z. John Zhang of the School of Chemistry and Biochemistry were among 60 researchers who received the 2002 Presidential Early Career Awards for Scientists and Engineers from President George Bush in July. The awards are the nation's highest honor for professionals working at the outset of their independent research careers.

The Human Factors and Ergonomics Society has awarded School of Psychology Professors Wendy Rogers and Dan Fisk the 2002 Best Ergonomics in Design Article award. Graduate students Amy Mykityshyn and Regan Campbell were also cited in the award. The team published research that shows that problems exist with the design of and instructions for various home medical devices.

C.P. Wong, a professor in the School of Materials Science and Engineering, received the 2002 Exceptional Technical Achievement Award from the Components, Packaging and Manufacturing Technology Society. He was cited for his pioneering work in polymeric materials for electronics packaging applications.


Also see Research Notes news stories.


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Last updated: Jan. 6, 2003