New theory may shed light on dynamics of large-polymer liquids

Aug 23, 2011
New theory may shed light on dynamics of large-polymer liquids
This is Illinois professor Kenneth S. Schweizer. Credit: L. Brain Stauffer

A new physics-based theory could give researchers a deeper understanding of the unusual, slow dynamics of liquids composed of large polymers. This advance provides a better picture of how polymer molecules respond under fast-flow, high-stress processing conditions for plastics and other polymeric materials.

Kenneth S. Schweizer, the G. Ronald and Margaret H. Professor of materials science and engineering at the University of Illinois, and graduate student Daniel Sussman published their findings in the journal .

"This is the first microscopic theory of entangled liquids at a fundamental force level which constructs the dynamic confinement potential that controls slow macromolecular motion," said Schweizer, who also is a professor of chemistry and of chemical and biomolecular engineering and is affiliated with the Frederick Seitz Laboratory at the U. of I. "Our breakthrough lays the foundation for an enormous amount of future work relevant to both the synthetic polymers of plastics engineering and the biopolymers relevant to cell biology and mechanics."

Polymers are long, large molecules that are ubiquitous in biology, chemistry and materials, from the stiff filaments that give cells their structure to plastics. Linear polymers fall into two classes: rigid rods like uncooked spaghetti or flexible strands like al dente noodles.

When in a dense solution, linear polymers become entangled like spaghetti in a pot, intertwining and crowding each other. Each polymer is hemmed in by its neighbors, so that the liquid behaves like an elastic, viscous rubber. Given enough time, the liquid will eventually flow slowly as polymers crawl along like snakes, a movement called reptation. Researchers have long assumed that each polymer's reptation is confined to a tube-shaped region of space, like a snake slithering through a pipe, but have had difficulty understanding how and why the polymers behave that way.

Schweizer and Sussman's new theory, based on microscopic physics, explains the slow dynamics of rigid entangled polymers and quantitatively constructs the confining dynamic tube from the forces between molecules. The tube concept emerges as a consequence of the strong interactions of a polymer with its myriad of intertwining neighbors. The theory's mathematical approach sheds greater light on entanglement and better explains experimental data.

"Our ability to take into account these crucial physical effects allows us to predict, not assume, the confining tube concept, identify its limitations, and predict how applied forces modify motion and elasticity," Schweizer said.

Not only does the new theory predict tube confinement and reptative motion, it reveals important limitations. The researchers found that the "tubes" weaken as applied forces increase, to the point where the tube concept fails completely and the liquid loses its rubbery nature. This is particularly important in plastics processing, which exposes polymer liquids to high stress conditions.

Next, the researchers plan to continue to study how external stress or strain quantitatively determine the driven mechanical flow behavior of entangled polymer liquids. They also hope to develop a theory for how attractive forces can compete with entanglement forces to result in soft polymer gels.

Explore further: New research predicts when, how materials will act

More information: The paper, "Microscopic Theory of the Tube Confinement Potential for Liquids of Topologically Entangled Rigid Macromolecules," is available online.

Related Stories

Muscle filaments make mechanical strain visible

Dec 20, 2010

Plastics-based materials have been in use for decades. But manufacturers are facing a serious hurdle in their quest for new developments: Substantial influences of the microscopic material structure on mechanical ...

Scientists de-polymerize polymers

Jun 26, 2007

Japanese scientists have created a process that breaks down certain plastics, allowing the chemicals to be reused to make new higher-quality plastic.

Researchers at UA developing next-gen conductive polymers

Dec 23, 2010

(PhysOrg.com) -- Conductive polymers, while not quite wonder materials, have the potential for being so and University of Akron polymer scientists and polymer engineers are focused on developing the next generation ...

Recommended for you

New filter could advance terahertz data transmission

Feb 27, 2015

University of Utah engineers have discovered a new approach for designing filters capable of separating different frequencies in the terahertz spectrum, the next generation of communications bandwidth that ...

The super-resolution revolution

Feb 27, 2015

Cambridge scientists are part of a resolution revolution. Building powerful instruments that shatter the physical limits of optical microscopy, they are beginning to watch molecular processes as they happen, ...

Precision gas sensor could fit on a chip

Feb 27, 2015

Using their expertise in silicon optics, Cornell engineers have miniaturized a light source in the elusive mid-infrared (mid-IR) spectrum, effectively squeezing the capabilities of a large, tabletop laser onto a 1-millimeter ...

A new X-ray microscope for nanoscale imaging

Feb 27, 2015

Delivering the capability to image nanostructures and chemical reactions down to nanometer resolution requires a new class of x-ray microscope that can perform precision microscopy experiments using ultra-bright ...

New research signals big future for quantum radar

Feb 26, 2015

A prototype quantum radar that has the potential to detect objects which are invisible to conventional systems has been developed by an international research team led by a quantum information scientist at the University ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.