Nav: Home

When it comes to polymer fragility, size does matter

October 18, 2016

WASHINGTON, D.C., October 18, 2016 -- Polymers are very large molecules consisting of thousands, even millions, of atoms bonded together in a repeating pattern similar to a chain. They make up many of the things around us we consider part of our everyday lives, from bottles and tires to airplanes and medical devices. Understanding what gives polymers their unique properties is helpful in developing new functional materials for various current and future technologies. A multinational team of researchers have brought together expertise and experimental results over years to help to explain the extremely strong temperature dependence of viscoelastic properties of polymers melts, a mystery that had thus far evaded explanation.

Fragility index is a parameter that quantifies how fast the material transforms from a solid to a liquid with temperature increase. For many years the higher fragility of polymers as compared to small molecules has been well documented. Many polymers exhibit fragility index approximately 1.5 times higher than even the most fragile, small molecular liquids and until now, there has been no clear answer as to why this is the case.

By combining a number of tools and techniques, a team of researchers from the U.S., Italy and China was able to find a more complete picture of the glass transition phenomenon in polymers and to point out where the polymers differ from small molecular liquids. The researchers explain their findings this week in The Journal of Chemical Physics, from AIP Publishing.

"We worked on this problem with our colleagues for a long time and though our paper with the similar title, 'Why many polymers are so fragile?' was published in 2007, we could only formulate the problem, we had no answer," explained Alexei P. Sokolov, a research scientist at Oak Ridge National Laboratory and professor of Chemistry and Physics at the University of Tennessee. "Over the years we accumulated many experimental results obtained by many different techniques (this is why the paper has so many authors) on a model polymer polystyrene to come up with this idea." This provided the broad view of many polymer specific properties needed to figure out what was missing. Using polystyrene with various chain lengths, researchers correlated many of their properties to their fragility and demonstrated that these correlations work for short chains but progressively fail when the length, i.e. the number of repeated units or segments, increases. The work may finally resolves this puzzle.

The researchers realized that the segmental (also called structural) relaxation in the case of polymers presents the relaxation of only a small part of the molecule. For polymers the complete molecular scale relaxation happens only on a much longer time scale that corresponds to chain relaxation. They show that analysis of the chain relaxation instead of relaxation of segments restores all the correlations characteristic for non-polymeric systems. This discovery leads to a new way of looking on the problem.

What does this mean for the polymers that are part of our daily life?

"Our work has broader implications, because similar mechanisms may account for rather high fragility of other complex systems in soft condensed matter," Sokolov said. "Whether this will help to make better polymers remains to be seen, but it should help in the design of polymers with the desired viscoelastic properties."
The article, "Why many polymers are so fragile: a new perspective," is authored by C. Dalle-Ferrier, A. Kisliuk, L. Hong, G. Carini Jr, G. Carini, G. D'Angelo, C. Alba-Simionesco, V.N. Novikov and A.P. Sokolov. The article will appear in the journal The Journal of Chemical Physics on October 18, 2016 (DOI: 10.1063/1.4964362). After that date, it can be accessed at


The Journal of Chemical Physics publishes concise and definitive reports of significant research in the methods and applications of chemical physics. See

American Institute of Physics

Related Polymers Articles:

Oyster shells inspire new method to make superstrong, flexible polymers
Columbia Engineers developed a method inspired by the nacre of oyster shells, a composite material with extraordinary mechanical properties, including great strength and resilience.
The brighter side of twisted polymers
A strategy to produce highly fluorescent nanoparticles through careful molecular design of conjugated polymers has been developed by KAUST researchers.
New strategy produces stronger polymers
MIT researchers have found a way to reduce the number of loops in polymer networks such as gels, plastics, and rubber.
Team highlights work on tuning block polymers for nanostructured systems
High-performance materials are enabling major advances in a wide range of applications from energy generation and digital information storage to disease screening and medical devices.
Estimating the glass transition temperature for polymers in 'confined geometries'
Polystyrene has a glass transition temperature of about 100 C -- at room temperature it behaves like a solid material.
Rapid Imaging of Polymers Could Lead to Better Bioimaging
A recent study by researchers at the Beckman Institute for Advanced Science and Technology at the University of Illinois identifies a method of Quantum Cascade Laser-based (QCL) infrared spectroscopic imaging that provides a more rapid method than conventional Fourier transform infrared imaging (FT-IR) to examine spherulites, large semicrystalline polymer samples, in order to identify chemical and structural properties.
Macromolecules: Light to design precision polymers
Chemists of Karlsruhe Institute of Technology have succeeded in specifically controlling the setup of precision polymers by light-induced chemical reactions.
International engineering team develop self-powered mobile polymers
n international group involving Inha University, University of Pittsburgh and the Air Force Research Laboratory has built upon their previous research and identified new materials that directly convert ultraviolet light into motion without the need for electronics or other traditional methods.
'Bottlebrush' polymers make dielectric elastomers increasingly viable for use in devices
A multi-institutional research team has developed a new electroactive polymer material that can change shape and size when exposed to a relatively small electric field.
NIST-made 'sun and rain' used to study nanoparticle release from polymers
In a recently published paper, researchers from the National Institute of Standards and Technology (NIST) describe how they subjected a commercial nanoparticle-infused coating to NIST-developed methods for accelerating the effects of weathering from ultraviolet (UV) radiation and simulated washings of rainwater.

Related Polymers Reading:

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Digital Manipulation
Technology has reshaped our lives in amazing ways. But at what cost? This hour, TED speakers reveal how what we see, read, believe — even how we vote — can be manipulated by the technology we use. Guests include journalist Carole Cadwalladr, consumer advocate Finn Myrstad, writer and marketing professor Scott Galloway, behavioral designer Nir Eyal, and computer graphics researcher Doug Roble.
Now Playing: Science for the People

#529 Do You Really Want to Find Out Who's Your Daddy?
At least some of you by now have probably spit into a tube and mailed it off to find out who your closest relatives are, where you might be from, and what terrible diseases might await you. But what exactly did you find out? And what did you give away? In this live panel at Awesome Con we bring in science writer Tina Saey to talk about all her DNA testing, and bioethicist Debra Mathews, to determine whether Tina should have done it at all. Related links: What FamilyTreeDNA sharing genetic data with police means for you Crime solvers embraced...