Science Daily — 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.

The Newvision Kampala Uganda:Wednesday, 25th April, 2007

ASTRONOMERS have found the most Earth-like planet outside the Solar System to date, a world which could have water running on its surface, the BBC reported yesterday.

The planet orbits the faint star Gliese 581, which is 20.5 light-years away in the constellation Libra.

Scientists made the discovery using the Eso 3.6m Telescope in Chile.
They say the benign temperatures on the planet mean any water there could exist in liquid form, and this raises the chances it could also harbour life.

“We have estimated that the mean temperature of this 'super-Earth’ lies between 0 and 40 degrees Celsius, and water would thus be liquid,” explained Stephane Udry of the Geneva Observatory, lead author of the scientific paper reporting the result. “Moreover, its radius should be only 1.5 times the Earth’s radius, and models predict that the planet should be either rocky - like our Earth - or covered with oceans.”

Xavier Delfosse, a member of the team from Grenoble University, added: “Liquid water is critical to life as we know it.”
He believes the planet may now become a very important target for future space missions dedicated to the search for extra-terrestrial life, including plants.

The exo-planet - as astronomers call planets around a star other than the Sun - is the smallest yet found, and completes a full orbit of its parent star in just 13 days. Indeed, it is 14 times closer to its star than the Earth is to our Sun.

However, given that the host star is smaller and colder than the Sun - and thus less luminous - the planet nevertheless lies in the “habitable zone,” the region around a star where water could be liquid.

Gliese 581 was identified at the European Southern Observatory (Eso) facility at La Silla in the Atacama Desert.

To make their discovery, researchers used a very sensitive instrument that can measure tiny changes in the velocity of a star as it experiences the gravitational tug of a nearby planet.

Astronomers are stuck with such indirect methods of detection because current telescope technology struggles to image very distant and faint objects - especially when they orbit close to the glare of a star.

The Gliese 581 system has now yielded three planets: the new super-Earth, a 15 Earth-mass planet orbiting even closer to the parent star, and an eight Earth-mass planet that lies further out.

The latest discovery has created tremendous excitement among scientists.
Of the more than 200 exoplanets so far discovered, a great many are Jupiter-like gas giants that experience blazing temperatures because they orbit close to hot stars.

The Gliese 581 super-Earth is in what scientists call the “Goldilocks Zone” where temperatures “are just right” for life to have a chance to exist.

Commenting on the discovery, Alison Boyle, the curator of astronomy at London’s Science Museum, said: “Of all the planets we’ve found around other stars, this is the one that looks as though it might have the right ingredients for life.

“It’s 20 light-years away and so we won’t be going there anytime soon, but with new kinds of propulsion technology that could change in the future. And obviously we'll be training some powerful telescopes on it to see what we can see,” she told BBC News.

“Is there life anywhere else?’ is a fundamental question we all ask.”