The polymers contain mechanically active molecules called mechanophores. When pushed or pulled with a certain force, specific chemical reactions are triggered in the mechanophores.
“This offers a new way to build function directly into synthetic materials,” said Nancy Sottos, a Willett Professor of materials science and engineering at the U. of I. “And it opens the door to creating mechanophores that can perform different responsive functions, including self-sensing and self-reinforcing, when stressed.”
In previous work, Sottos and collaborators showed they could use mechanical force to induce a reaction in mechanophore-linked polymers that were in solution. Now, as reported in the May 7 issue of the journal Nature, the researchers show they can perform a similar feat in a solid polymer.
Mechanically induced chemical activation (also known as mechanochemical transduction) enables an extraordinary range of physiological processes, including the senses of touch, hearing and balance, as well as growth and remodeling of tissue and bone.
Analogous to the responsive behavior of biological systems, the channeling of mechanical energy to selectively trigger a reaction that alters or enhances a material’s properties is being harnessed by the U. of I. researchers.
In critical material systems, such as polymers used in aircraft components self-sensing and self-reinforcing capabilities could be used to report damage and warn of potential component failure, slow the spread of damage to extend a material’s lifetime, or even repair damage in early stages to avoid catastrophic failure.
“By coupling mechanical energy directly to structural response, the desired functionality could be precisely linked to the triggering stimulus,” said Sottos, who also is affiliated with the university’s Beckman Institute.
In their work, the researchers used molecules called spiropyrans, a promising class of molecular probes that serve as color-generating mechanophores, capable of vivid color changes when they undergo mechanochemical change. Normally colorless, the spiropyran used in the experiments turns red or purple when exposed to certain levels of mechanical stress.
“Mechanical stress induces a ring-opening reaction of the spiropyran that changes the color of the material,” said Douglas Davis, a graduate research assistant and the paper’s lead author. “The reaction is reversible, so we can repeat the opening and closing of the mechanophore.”
“Spiropyrans can serve as molecular probes to aid in understanding the effects of stress and accumulated damage in polymeric materials, thereby providing an opportunity for assessment, modification and improvement prior to failure,” Davis said.
To demonstrate the mechanochemical response, the researchers prepared two different mechanophore-linked polymers and subjected them to different levels of mechanical stress.
In one polymer, an elastomer, the material was stretched until it broke in two. A vivid color change in the polymer occurred just before it snapped.
The second polymer was formed into rigid beads several hundred microns in diameter. When the beads were squeezed, they changed from colorless to purple.
The color change that took place within both polymers could serve as a good indicator of how much stress a mechanical part or structural component made of the material had undergone.
“We’ve moved very seamlessly from chemistry to materials, and from materials we are now moving into engineering applications,” Sottos said. “With a deeper understanding of mechanophore design rules and efficient chemical response pathways, we envision new classes of dynamically responsive polymers that locally remodel, reorganize or even regenerate via mechanical regulation.”
In addition to Sottos and Davis, the paper’s co-authors include materials science and engineering professor Paul Braun, chemistry professors Todd Martinez and Jeffrey Moore, and aerospace engineering professor Scott White, as well as members of their research groups.
The work was funded by the U.S. Army Research Office MURI program.
Editor’s notes: To reach Nancy Sottos, call 217-333-1041; e-mail: firstname.lastname@example.org.Video showing force-induced color change in a mechanophore cross-linked polymer bead under compressive loading (left) and corresponding force-displacment curve (right).
James E. Kloeppel | Newswise Science News
'Frequency combs' ID chemicals within the mid-infrared spectral region
16.03.2018 | American Institute of Physics
Fraunhofer HHI have developed a novel single-polarization Kramers-Kronig receiver scheme
16.03.2018 | Fraunhofer-Institut für Nachrichtentechnik, Heinrich-Hertz-Institut, HHI
Animal photoreceptors capture light with photopigments. Researchers from the University of Göttingen have now discovered that these photopigments fulfill an...
On 15 March, the AWI research aeroplane Polar 5 will depart for Greenland. Concentrating on the furthest northeast region of the island, an international team...
The world’s second-largest ice shelf was the destination for a Polarstern expedition that ended in Punta Arenas, Chile on 14th March 2018. Oceanographers from...
At the 2018 ILA Berlin Air Show from April 25–29, the Fraunhofer Institute for Laser Technology ILT is showcasing extreme high-speed Laser Material Deposition (EHLA): A video documents how for metal components that are highly loaded, EHLA has already proved itself as an alternative to hard chrome plating, which is now allowed only under special conditions.
When the EU restricted the use of hexavalent chromium compounds to special applications requiring authorization, the move prompted a rethink in the surface...
At the ILA Berlin, hall 4, booth 202, Fraunhofer FHR will present two radar sensors for navigation support of drones. The sensors are valuable components in the implementation of autonomous flying drones: they function as obstacle detectors to prevent collisions. Radar sensors also operate reliably in restricted visibility, e.g. in foggy or dusty conditions. Due to their ability to measure distances with high precision, the radar sensors can also be used as altimeters when other sources of information such as barometers or GPS are not available or cannot operate optimally.
Drones play an increasingly important role in the area of logistics and services. Well-known logistic companies place great hope in these compact, aerial...
16.03.2018 | Event News
13.03.2018 | Event News
08.03.2018 | Event News
16.03.2018 | Earth Sciences
16.03.2018 | Physics and Astronomy
16.03.2018 | Life Sciences