Researchers at the University of Illinois have developed a theory that predicts how these materials age. The theory also explains why motions at the molecular level can have macroscopic consequences.
Three years ago, Schweizer and graduate student Erica Saltzman developed a theory that described the transition upon cooling of a polymeric material from a liquid to an amorphous solid or glass. The theory explained how the viscosity of a polymer glass changes dramatically over a narrow temperature range. The researchers reported that work in the July 22, 2004, issue of the Journal of Chemical Physics.
Now, in the April 20 issue of Physical Review Letters, Schweizer and postdoctoral research associate Kang Chen present a theory to describe the aging process in polymer glasses. The new theory predicts not only how polymer molecules move, but also the material properties, at a wide variety of times and temperatures.
Polymer glasses are plastics that possess unusual and technologically useful mechanical properties. Unlike most other types of solids, polymer glasses can possess high impact resistance and, even though they are stiff, can often be significantly deformed without breaking. They are usually inexpensive to make, and easily melted and molded into many shapes.
And, they're always on the move.
Unlike window glass, which melts at roughly 1,200 degrees above room temperature, polymer glasses have melting points much closer to room temperature. So close, in fact, that many polymer glasses retain some liquid-like properties at room temperature, including motion at the molecular level.
"The movements are so small and so slow, we can't see them without the aid of sophisticated measuring tools," Schweizer said. "Nevertheless, this residual motion can significantly change the material's mechanical and thermal properties over time."
As the material gradually reconfigures and approaches equilibrium at room temperature, the movements become slower and slower. Under sufficiently cold conditions, this "relaxation" time can become astronomically large, even longer than the age of the universe for some materials.
"Among other possible effects, the aging process causes polymer glasses to become stiffer and often more brittle," said Schweizer, who also is a professor of chemistry, of chemical and biomolecular engineering, and a researcher at the university's Frederick Seitz Materials Research Laboratory.
Over time, the molecules crowd closer together, increasing the density and changing the mechanical properties of the material.
"Through our theory we developed a way to relate the physical properties of a polymer glass to the time scale of molecular movement," Schweizer said. "This information is especially important in engineering applications where small changes in dimensions, stiffness or other properties can affect long-term performance or reliability."
The work was funded by the National Science Foundation.Editor's note: To reach Kenneth Schweizer, call 217-333-6440; e-mail:
James E. Kloeppel | University of Illinois
A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne
Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)
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
23.06.2017 | Physics and Astronomy
23.06.2017 | Physics and Astronomy
23.06.2017 | Information Technology