Anyone who's stuffed a smart phone in their back pocket would appreciate the convenience of electronic devices that could bend. Flexible electronics could spawn new products: clothing wired to cool or heat, reading tablets that could fold like newspaper, and so on.
Alas, electronic components such as chips, displays and wires are generally made from metals and inorganic semiconductors -- materials with physical properties that make them fairly stiff and brittle.
In the quest for flexibility many researchers have been experimenting with semiconductors made from plastics or, more accurately polymers, which bend and stretch readily enough.
"But at the molecular level polymers look like a bowl of spaghetti," says Stanford chemical engineering professor Andrew Spakowitz, adding: "Those non-uniform structures have important implications for the conductive properties of polymeric semiconductors."
Spakowitz and two colleagues, Rodrigo Noriega, a postdoctoral researcher at UC Berkeley, and Alberto Salleo, a Stanford professor of Materials Science and Engineering, have created the first theoretical framework that includes this molecular-level structural inhomogeneity, seeking to understand, predict and improve the conductivity of semiconducting polymers.
Their theory, published today (Monday Sept 23@12 pm PST) in the Proceedings of the National Academy of Sciences, deals with the observed tendency of polymeric semiconductors to conduct electricity at differing rates in different parts of the material – a variability that, as the Stanford paper explains, turns out to depend on whether the polymer strands are coiled up like a bowl of spaghetti or run relatively true, even if curved, like lanes on a highway.
In other words, the entangled structure that allows plastics and other polymers to bend also impedes their ability to conduct electricity, whereas the regular structure that makes silicon semiconductors such great electrical switches tends to make it a bad fit for our back pockets.The Stanford paper in PNAS gives experimental researchers a model that allows them to understand the tradeoff between the flexibility and conductivity of polymeric semiconductors.
But it was only in the late 1970s that a trio of scientists discovered that plastics which, until then were considered non-conductive materials suitable to wrap around wires for insulation could, under certain circumstances, be induced to conduct electricity.
The three scientists, Alan Heeger, Alan MacDiarmid and Hideki Shirakawa, shared the Nobel Prize in Chemistry in 2000 for their co-discovery of polymeric semiconductors. In recent years, with increasing urgency, researchers have been trying to harness the finicky electrical properties of plastics with an eye toward fashioning electronics that will bend without breaking.
In the process of experimenting with polymeric semiconductors, however, researchers discovered that these flexible materials exhibited "anomalous transport behavior" or, simply put, variability in the speed at which electrons flowed through the system.One of the fundamental insights of the Stanford paper is that electron flow through polymers is affected by their spaghetti-like structure – a structure that is far less uniform than that of the various forms of silicon and other inorganic semiconductors whose electrical properties are much better understood.
In essence, the variability of electron flow through polymeric semiconductors owes to the way the structure of these molecular chains creates fast paths and congestion points (refer to diagram). In a stylized sense imagine that a polymer chain runs relatively straight before coming to a hairpin turn to form a U-shape. An electric field moves electrons rapidly up to the hairpin, only to stall.
Meanwhile imagine a similar U-shape polymer separated from the first by a tiny gap. Eventually, the electrons will jump that gap to go from the first fast path to the opposing fast path. One way to think about this is a traffic analogy, in which the electrons must wait for a traffic light to cross from one street, though the gap, before proceeding down the next.
Most importantly, perhaps, in terms of putting this knowledge to use, the Stanford theory includes a simple algorithm that begins to suggest how to control the process for making polymers – and devices out of the resulting materials - with an eye toward improving their electronic properties.
"There are many, many types of monomers and many variables in the process," Spakowitz said. The model presented by the Stanford team simplifies this problem greatly by reducing it to a small number of variables describing the structural and electronic properties of semiconducting polymers. This simplicity does not preclude its predictive value; in fact, it makes it possible to evaluate the main aspects describing the physics of charge transport in these systems.
"A simple theory that works is a good start," said Spakowitz, who envisions much work ahead to bring bending smart phones and folding e-readers to reality.
Media Contact: Tom Abate, Associate Director of Communications, Stanford Engineering, 650-736-2245, email@example.com
Tom Abate | EurekAlert!
How protons move through a fuel cell
22.06.2017 | Empa - Eidgenössische Materialprüfungs- und Forschungsanstalt
Fraunhofer IZFP acquires lucrative EU project for increasing nuclear power plant safety
21.06.2017 | Fraunhofer-Institut für Zerstörungsfreie Prüfverfahren IZFP
An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.
Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...
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...
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...
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...
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)...
19.06.2017 | Event News
13.06.2017 | Event News
13.06.2017 | Event News
22.06.2017 | Life Sciences
22.06.2017 | Materials Sciences
22.06.2017 | Materials Sciences