New Theory Explains Nonlinear Stretching in Rubbery Materials


Professor of Physics Paul Goldbart, in collaboration with Xiangjun Xing (Syracuse) and Leo Radzihovsky (Colorado), has solved a theory problem that has puzzled physicists since the 1940s (Phys. Rev. Lett. 98, 075502 [2007]).

Measuring the force produced by stretching a rubber band to its limits is easy, but the standard theory of rubbery materials cannot predict this force.

When they are not stretched too much, rubbery materials act as simple springs, obeying Hooke's law. Thus, a 10-percent increase in stretching force will extend a typical rubber band 10 percent farther. But at greater stretching forces, that simple linear relation fails. The existence of the nonlinearity has long been known, but understanding its origins and developing a theory that correctly captures it "has been a challenge to the physics community for 60 years," said Goldbart.

By including the extra entropy associated with long length-scale motion while simultaneously coping with the essentially incompressible nature of rubbery materials, the researchers are now able to construct a theory that agrees with experiment, not only in the Hookean regime but also beyond—deep into the nonlinear regime. Read more...

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Assistant Professors Jessie Shelton and Benjamin Hooberman of the Department of Physics at the University of Illinois Urbana-Champaign have been selected for 2017 DOE Early Career Awards. They are among 65 early-career scientists nationwide to receive the five-year awards through the Department of Energy Office of Science’s Early Career Research Program, now in its second year. According to the DOE, this year’s awardees were selected from a pool of about 1,150 applicants, working in research areas identified by the DOE as high priorities for the nation.

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The most intriguing and relevant science happens at the highest levels of scientific pursuit-at major research universities and laboratories, far above and beyond typical high-school science curriculum. But this summer, 12 rising high school sophomores, juniors, and seniors-eight from Centennial and four from Central High Schools, both in Champaign-had the rare opportunity to partake in cutting-edge scientific research at a leading research institution.

The six-week summer-research Young Scholars Program (YSP) at the University of Illinois at Urbana-Champaign was initiated by members of the Nuclear Physics Laboratory (NPL) group, who soon joined forces with other faculty members in the Department of Physics and with faculty members of the POETS Engineering Research Center.

Imagine planting a single seed and, with great precision, being able to predict the exact height of the tree that grows from it. Now imagine traveling to the future and snapping photographic proof that you were right.

If you think of the seed as the early universe, and the tree as the universe the way it looks now, you have an idea of what the Dark Energy Survey (DES) collaboration has just done. In a presentation today at the American Physical Society Division of Particles and Fields meeting at the U.S. Department of Energy’s (DOE) Fermi National Accelerator Laboratory, DES scientists will unveil the most accurate measurement ever made of the present large-scale structure of the universe.

These measurements of the amount and “clumpiness” (or distribution) of dark matter in the present-day cosmos were made with a precision that, for the first time, rivals that of inferences from the early universe by the European Space Agency’s orbiting Planck observatory. The new DES result (the tree, in the above metaphor) is close to “forecasts” made from the Planck measurements of the distant past (the seed), allowing scientists to understand more about the ways the universe has evolved over 14 billion years.

“This result is beyond exciting,” said Scott Dodelson of Fermilab, one of the lead scientists on this result. “For the first time, we’re able to see the current structure of the universe with the same clarity that we can see its infancy, and we can follow the threads from one to the other, confirming many predictions along the way.”

It took two years on a supercomputer to simulate 1.2 microseconds in the life of the HIV capsid, a protein cage that shuttles the HIV virus to the nucleus of a human cell. The 64-million-atom simulation offers new insights into how the virus senses its environment and completes its infective cycle.

The findings are reported in the journal Nature Communications.