Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Study sets benchmark properties for popular conducting plastic

31.03.2006


Results essential to optimize materials for diverse applications


Atomic force microscopy image of aligned nanofibrils of a highly conducting plastic. Each nanofibril is made of stacks of regioregular polythiophene (RRP) molecules. Charge carriers move particularly well along the...



Steadily increasing the length of a purified conducting polymer vastly improves its ability to conduct electricity, report researchers at Carnegie Mellon University, whose work appeared March 22 in the Journal of the American Chemical Society. Their study of regioregular polythiophenes (RRPs) establishes benchmark properties for these materials that suggest how to optimize their use for a new generation of diverse materials, including solar panels, transistors in radio frequency identification tags, and light-weight, flexible, organic light-emitting displays.

"We found that by growing very pure, single RRP chains made of uniform small units, we dramatically increased the ability of these polymers to conduct electricity," said Richard D. McCullough, who initially discovered RRPs in 1992. "This work establishes basic properties that researchers everywhere need to know to create new, better conducting plastics. In fact, designing materials based on these results could completely revolutionize the printable electronics industry."


"Our results are very significant, since they cast new light on the mechanism by which polymers conduct electricity," said Tomasz Kowalewski, associate professor of chemistry and senior author on the study.

Unlike plastics that insulate, or prevent, the flow of electrical charges, conducting plastics actually facilitate current through their nanostructure. Conducting plastics are the subject of intense research, given that they could offer light-weight, flexible, energy-saving alternatives for materials used in solar panels and screen displays. And because they can be dissolved in solution, affixed to a variety of templates like silicon and manufactured on an industrial scale, RRPs are considered among the most promising conducting plastics in nanotech research today, according to McCullough, dean of the Mellon College of Science and professor of chemistry.

"Our tests showed that highly uniform RRPs self-assemble into well-defined elongated aggregates called nanofibrils, which stack one against the other," Kowalewski said. "About 5,000 of these nanofibrils would fit side by side in the width of a human hair. The presence of these well-defined structures allowed us for the first time to make a connection between the size of polymer molecules, the type of structure they form and the ease with which current can move through nanofibril aggregates." (See image.)

The vast improvement in conductivity is tied to several key properties that were unambiguously shown for the first time in this study, according to Kowalewski.

"We made the key discovery that mobility -- how easily electrons move -- increases exponentially as the width of a nanofibril increases," Kowalewski said. Each rope-like nanofibril actually is a stack of RRP molecules, so the longer these molecules, the wider the nanofibril and the faster the electrical conductivity. (See image insert of RRP stacks.) In this way, electricity moves preferably perpendicular through the rows of naturally aligned nanofibrils.

"We found that charge carriers encounter fewer hurdles when jumping between wider nanofibrils," said Kowalewski. "Ultimately through this study, we found that the nanostructure of our conducting plastic profoundly enhances its ability to conduct electricity."

Conductivity increases with the length of an RRP molecule -- and hence the width of each nanofibril -- because it takes less time for a charge carrier to cross through wider nanofibrils than narrower ones. (Charge carriers are unbound particles that carry an electric charge through a molecular structure). All this can be tied to the fact that a charge carrier that enters a short molecule disrupts its energetic environment considerably more than if that same charge carrier enters a long molecule. This energetic hurdle, called reorganization energy, thus slows the movement of charge carriers that move from short molecule to short molecule. The energetic hurdle is lower for a long molecule, which can absorb changes to its electrical environment more easily. This phenomenon could be one of the reasons why charge carriers jump more quickly from long molecule to long molecule, according to Kowalewski.

"We hope that these findings will stimulate further theoretical and experimental work which will significantly improve the performance of polymer-based electronics and open the way to a wide range of applications," Kowalewski said.

To show that increasing the width of RRP nanofibrils exponentially increased charge carrier mobility, the Carnegie Mellon team first created pure RRPs of uniform size, or molecular weight. Next, they placed the drops of RRPs dissolved in a solvent onto silicon chips whose surfaces were specially prepared for use as nanotransistors. Such "drop casting" allowed the team to create a series of nanostructures that varied in accordance with the length of the RRP chains initially present in solution.

The team ran a current through these different RRP-based nanotransistors to measure their ability to conduct electricity. They used atomic force microscopy and a technique called grazing-incidence small-angle X-ray scattering to verify that periodic, stacked structure of different RRPs indeed formed nanofibrils of corresponding widths. The latter technique was performed using the High Energy Synchrotron Source at Cornell University.

The team of investigators included students Rui Zhang in the Department of Chemistry; Bo Li in the laboratory of David Lambeth, professor of electrical and computer engineering; and faculty from the Department of Physics, who participated in X-ray scattering studies.

Lauren Ward | EurekAlert!
Further information:
http://www.cmu.edu

More articles from Materials Sciences:

nachricht Rice U. chemists create 3-D printed graphene foam
22.06.2017 | Rice University

nachricht Development of low-dimensional nanomaterials could revolutionize future technologies
19.06.2017 | DOE/Ames Laboratory

All articles from Materials Sciences >>>

The most recent press releases about innovation >>>

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

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

Im Focus: Optoelectronic Inline Measurement – Accurate to the Nanometer

Germany counts high-precision manufacturing processes among its advantages as a location. It’s not just the aerospace and automotive industries that require almost waste-free, high-precision manufacturing to provide an efficient way of testing the shape and orientation tolerances of products. Since current inline measurement technology not yet provides the required accuracy, the Fraunhofer Institute for Laser Technology ILT is collaborating with four renowned industry partners in the INSPIRE project to develop inline sensors with a new accuracy class. Funded by the German Federal Ministry of Education and Research (BMBF), the project is scheduled to run until the end of 2019.

New Manufacturing Technologies for New Products

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

Hubble captures massive dead disk galaxy that challenges theories of galaxy evolution

22.06.2017 | Physics and Astronomy

New femto-camera with quadrillion fractions of a second resolution

22.06.2017 | Physics and Astronomy

Rice U. chemists create 3-D printed graphene foam

22.06.2017 | Materials Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>