Sustainable Polymers of the Future May Come from New Theory

Tomorrow's specialty plastics may be produced more precisely and cheaply thanks to the apparently tight merger of a theory by a University of Oregon chemist and years of unexplained data from real world experiments involving polymers in Europe.

The work, which researchers believe may lead to a new class of materials, is described in a paper appearing in the Dec. 18 issue of the Journal of Physical Chemistry B (online Dec. 11). The findings eventually could prove useful in the fields of engineering, nanotechnology, renewable energy and, potentially, medicine, because proteins, DNA, RNA and other large molecules within cells may well move in the same way as those in plastics.

Traditional theory behind the processing of plastic materials since the 1960s has focused on the movement of individual macromolecules as they move by one another. Materials researchers, under this approach, end up with poorly understood products and unexplained data. The new theory of cooperative motion in liquids of polymers successfully explains these observations by considering the coordinated motion of macromolecules with their surrounding neighbors. The end result could remove guesswork and the costly, time-consuming testing of thousands of samples at various stages of production.

"The level of agreement between the data and the theory is remarkable," said Marina G. Guenza, a professor of theoretical physical chemistry at the UO. "We are making the connection between the chemistry of molecules and how they behave. It is really fundamental science. Our findings are exciting for experimentalists because we can see phenomena that they cannot understand. This theory is now explaining what is happening inside their samples. They are no longer dealing with just a set of data; our theory provides a picture of what is happening."

Guenza simplifies her mathematics-heavy theory -- built on Langevin equations that describe the movement of particles in liquid or gas -- to watching students disembark from a crowded bus. Any one student wanting to exit is stuck in place -- or meanders randomly in available spaces -- until other students begin moving toward the exit. As students organize into a group they become coordinated and speed their departure.

The theory addresses the often-seen subdiffusive behavior of molecules as they begin to form a glass under processing -- explaining why molecules slow and freeze into disorganized structures rather than ordering into a crystal, Guenza said. "We would really like to be able to control the properties of the material so that we can tailor the synthesis to achieve exact results."

The theory was put to the test under a variety of scenarios in labs in Germany, France and Switzerland after German plastics researcher Dieter Richter of the Max Planck Institute for Solid State Research, a co-author on the paper, approached Guenza after a conference session and said he had unexplained data that might be explained by Guenza's theory. The unexplained data and Guenza's theory merged under examination, which included the use of neutron spin-echo spectroscopy, a high-energy resolution-scattering technique.

"If you look at just one polymer, as is the case under conventional theory, you don't see any anomalous motion," said Guenza, whose research is funded by the National Science Foundation and the Petroleum Research Fund. "You don't see slowing one molecule alternating between slow and fast motion. Only if you treat the dynamics of a group of molecules together can you predict anomalous behaviors. That's what my theory can give you."

The theory now is being applied to other experiments to test its application to other anomalies, said Guenza, who is a member of three UO interdisciplinary institutes: the Institute of Theoretical Science; the Materials Science Institute and the Institute of Molecular Biology.

Co-authors of the paper with Guenza and Richter were Richter's colleagues M. Zamponi, A. Wischnewski, M. Monkenbusch and L. Willner, and researchers P. Falus and B. Farago, both of the Institut Laue-Langevin, a leading international neutron research center in Grenoble, France.