Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Theory predicts aging process in DVDs, plexiglas, other polymer glasses

24.04.2007
Polymer glasses are versatile plastics widely used in applications ranging from aircraft windshields to DVDs.

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.

"Glasses, including polymer glasses, are essentially frozen liquids,"
said Kenneth S. Schweizer, the G. Ronald and Margaret H. Morris Professor of Materials Science at the University of Illinois. "They appear solid, but because they are frozen liquids, the molecules continually undergo small motions that lead to a time dependence of properties."

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:
kschweiz@uiuc.edu.

James E. Kloeppel | University of Illinois
Further information:
http://www.news.uiuc.edu/news/07/0423aging.html

More articles from Physics and Astronomy:

nachricht From rocks in Colorado, evidence of a 'chaotic solar system'
23.02.2017 | University of Wisconsin-Madison

nachricht Prediction: More gas-giants will be found orbiting Sun-like stars
22.02.2017 | Carnegie Institution for Science

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

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

Im Focus: Safe glide at total engine failure with ELA-inside

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded after a glide flight with an Airbus A320 in ditching on the Hudson River. All 155 people on board were saved.

On January 15, 2009, Chesley B. Sullenberger was celebrated world-wide: after the two engines had failed due to bird strike, he and his flight crew succeeded...

Im Focus: Breakthrough with a chain of gold atoms

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

In the field of nanoscience, an international team of physicists with participants from Konstanz has achieved a breakthrough in understanding heat transport

Im Focus: DNA repair: a new letter in the cell alphabet

Results reveal how discoveries may be hidden in scientific “blind spots”

Cells need to repair damaged DNA in our genes to prevent the development of cancer and other diseases. Our cells therefore activate and send “repair-proteins”...

Im Focus: Dresdner scientists print tomorrow’s world

The Fraunhofer IWS Dresden and Technische Universität Dresden inaugurated their jointly operated Center for Additive Manufacturing Dresden (AMCD) with a festive ceremony on February 7, 2017. Scientists from various disciplines perform research on materials, additive manufacturing processes and innovative technologies, which build up components in a layer by layer process. This technology opens up new horizons for component design and combinations of functions. For example during fabrication, electrical conductors and sensors are already able to be additively manufactured into components. They provide information about stress conditions of a product during operation.

The 3D-printing technology, or additive manufacturing as it is often called, has long made the step out of scientific research laboratories into industrial...

Im Focus: Mimicking nature's cellular architectures via 3-D printing

Research offers new level of control over the structure of 3-D printed materials

Nature does amazing things with limited design materials. Grass, for example, can support its own weight, resist strong wind loads, and recover after being...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Booth and panel discussion – The Lindau Nobel Laureate Meetings at the AAAS 2017 Annual Meeting

13.02.2017 | Event News

Complex Loading versus Hidden Reserves

10.02.2017 | Event News

International Conference on Crystal Growth in Freiburg

09.02.2017 | Event News

 
Latest News

New pop-up strategy inspired by cuts, not folds

27.02.2017 | Materials Sciences

Sandia uses confined nanoparticles to improve hydrogen storage materials performance

27.02.2017 | Interdisciplinary Research

Decoding the genome's cryptic language

27.02.2017 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>