Nav: Home

Polymers to give early warning signs

April 24, 2019

Researchers at the University of Fribourg's Adolphe Merkle Institute (AMI) and Hokkaido University in Japan have developed a method to tailor the properties of stress-indicating molecules that can be integrated into polymers and signal damages or excessive mechanical loads with an optical signal.

As part of their research activities within the National Center of Competence in Research Bio-inspired Materials, Professor Christoph Weder, the chair of Polymer Chemistry and Materials at AMI, and his team are investigating polymers that change their color or fluorescence characteristics when placed under mechanical load. The prevailing approach to achieve this function is based on specifically designed sensor molecules that contain weak chemical bonds that break when the applied mechanical force exceeds a certain threshold. This effect can cause a color change or other pre-defined responses. A fundamental limitation of this approach, however, is that the weak bonds can also break upon exposure to light or heat. This lack of specificity reduces the practical usefulness of stress-indicating polymers. It normally also makes the effect irreversible.

Addressing this problem, Weder and Dr. Yoshimitsu Sagara - a Japanese researcher who spent two years in Weder's group at AMI before joining Hokkaido University as an Assistant Professor - devised a new type of sensor molecule that can only be activated by mechanical force. Unlike in previous force-transducing molecules, no chemical bond breaking takes place. Instead, the new sensor molecules consist of two parts that mechanically interlocked. This interconnection prevents the separation of the two parts, while still allowing them to be pushed together or pulled away from each other. Such molecular pushing and pulling causes the molecule's fluorescence to change from off to on.

In a new publication in the open-access journal ACS Central Science, Weder, Sagara, and their co-workers report that this new concept is robust and versatile. "The design approach allows one to tailor the properties of such sensor molecules, as their behavior is quite predictable," explains Weder. "We chose to demonstrate this by tackling materials that display white fluorescence when stretched," adds Sagara. "Mechanoresponsive white fluorescence is in general difficult to achieve. It requires the combination of three sensor molecules with pre-defined emission colors: blue, green, and red (or orange). In addition, the sensor molecules also need to exhibit a similar response to mechanical stress to achieve ON/OFF switching of white emission when they are blended."

As intended, polymers containing the new motifs do not fluoresce in the absence of mechanical force, but they become brightly fluorescent - red, green, or blue, when only one type of sensor molecule was used, white when they were combined - when stretched. Because no chemical bonds are broken, the process is also fully reversible. Thus, when the new sensor molecules were incorporated in an elastic polymer, the fluorescence was turned on when the material was stretched, and turned off when the force was removed and the material contracted. Moreover, the fluorescence intensity, or brightness, was shown to correlate with the extent of deformation.

Potential applications for such materials include built-in monitors that send visual warning signs before a part fails, or that enable engineers to map stresses in parts under load and help them design these better. The sensor molecules also promise to be useful for fundamental, molecular-level investigations of stress-transfer mechanisms in synthetic materials as well as in biological systems.

The Swiss-Japanese team is currently collaborating to further simplify the design for an expansion of the concept to materials that change their color, instead of their fluorescence. The response of such motifs could be inspected without any auxiliary means and would thus be more useful for practical applications.
-end-
The research was funded by the Japan Science Technology Agency and the Swiss National Center of Competence in Research Bio-Inspired Materials.

Hokkaido University

Related Polymers Articles:

Theoretical tubulanes inspire ultrahard polymers
Rice University engineers print 3D blocks based on theoretical tubulanes and find they're nearly as hard as diamond.
New synthesis method yields degradable polymers
MIT chemists have come up with a way to make certain drug-delivery polymers more readily degradable by adding a novel type of building block to the polymer backbone.
Bottom-up synthesis of crystalline 2D polymers
Scientists at TU Dresden and Ulm University have succeeded in synthesizing sheet-like 2D polymers by a bottom-up process for the first time.
Secret messages hidden in light-sensitive polymers
Scientists from the CNRS and Aix-Marseille Université have recently shown how valuable light-sensitive macromolecules are: when exposed to the right wavelength of light, they can be transformed so as to change, erase or decode the molecular message that they contain.
Successful application of machine learning in the discovery of new polymers
As a powerful example of how artificial intelligence (AI) can accelerate the discovery of new materials, scientists in Japan have designed and verified polymers with high thermal conductivity -- a property that would be the key to heat management, for example, in the fifth-generation (5G) mobile communication technologies.
How to capture waste heat energy with improved polymers
By one official estimate, American manufacturing, transportation, residential and commercial consumers use only about 40 percent of the energy they draw on, wasting 60 percent.
Researchers can now predict properties of disordered polymers
Thanks to a team of researchers from the University of Illinois at Urbana-Champaign and the University of Massachusetts Amherst, scientists are able to read patterns on long chains of molecules to understand and predict behavior of disordered strands of proteins and polymers.
Synthesis of helical ladder polymers
Researchers at Kanazawa University synthesized helical ladder polymers with a well-defined cyclic repeating unit and one-handed helical geometry, as they reported in the Journal of the American Chemical Society.
Polymers jump through hoops on pathway to sustainable materials
Recyclable plastics that contain ring-shaped polymers may be a key to developing sustainable synthetic materials.
Polymers to give early warning signs
Researchers at the University of Fribourg's Adolphe Merkle Institute (AMI) and Hokkaido University in Japan have developed a method to tailor the properties of stress-indicating molecules that can be integrated into polymers and signal damages or excessive mechanical loads with an optical signal.
More Polymers News and Polymers Current Events

Top Science Podcasts

We have hand picked the top science podcasts of 2019.
Now Playing: TED Radio Hour

In & Out Of Love
We think of love as a mysterious, unknowable force. Something that happens to us. But what if we could control it? This hour, TED speakers on whether we can decide to fall in — and out of — love. Guests include writer Mandy Len Catron, biological anthropologist Helen Fisher, musician Dessa, One Love CEO Katie Hood, and psychologist Guy Winch.
Now Playing: Science for the People

#541 Wayfinding
These days when we want to know where we are or how to get where we want to go, most of us will pull out a smart phone with a built-in GPS and map app. Some of us old timers might still use an old school paper map from time to time. But we didn't always used to lean so heavily on maps and technology, and in some remote places of the world some people still navigate and wayfind their way without the aid of these tools... and in some cases do better without them. This week, host Rachelle Saunders...
Now Playing: Radiolab

Dolly Parton's America: Neon Moss
Today on Radiolab, we're bringing you the fourth episode of Jad's special series, Dolly Parton's America. In this episode, Jad goes back up the mountain to visit Dolly's actual Tennessee mountain home, where she tells stories about her first trips out of the holler. Back on the mountaintop, standing under the rain by the Little Pigeon River, the trip triggers memories of Jad's first visit to his father's childhood home, and opens the gateway to dizzying stories of music and migration. Support Radiolab today at Radiolab.org/donate.