Materials break, then remake, bonds to build strength

Aug 04, 2013

Microscopic tears in a new kind of man-made material may actually help the substance bulk up like a bodybuilder at the gym.

"We've shown how normally destructive can be channeled to bring about stronger ," said Duke chemist Steve Craig, who led the research. "The material responses are like Silly Putty transforming into a solid as stiff as the cap of a pen or a runny liquid transforming into soft Jell-O."

Scientists could one day use the stress-induced strength from these new materials to make better fluids such as , or soft-structure substances such as artificial heart valves. Materials like this wear out over time because of the repeated mechanical forces they experience during use. But Craig said if a material had properties to slow down its destruction, it would greatly improve quality of life.

It is the first time scientists have used force-induced chemistry within a material to make it stronger in response to stress. The results appear Monday, Aug. 5, 2013, in Nature Chemistry.

In past experiments, Craig's team has gripped and tugged on individual molecules of a material to see how it reacted at the . Now, the scientists have scaled up the material to contort it macroscopically and see how it responds.

Craig said the response is similar to what happens when a person lifts weights. Those individual stresses trigger biological processes in the muscles that ultimately increase the person's strength.

"It's the same idea chemists would like to use for ," he said. "Everyday materials can wear out with repeated stress. Think of your favorite t-shirt or even the oil in your . Wear after wear, fire after fire, these materials break down."

The new man-made materials Craig's team is making have characteristics already in place so that when a stress triggers a bond to break, it breaks in a way that triggers a subsequent reaction forcing the busted to reform new ones.

"It's like snapping a string. But before the string snaps, sites along it form so that when it breaks it can become tied to another string," Craig said.

The scientists first stressed one of the test materials by pulsing high-intensity sound waves through them. The sound waves create bubbles, which typically collapse and break the bonds of the molecules in the material. The forces breaking atoms in the new materials, however, triggered the formation of new bonds, which strengthened the liquid by transforming it into a soft Jell-O consistency.

To test the strength-building ability of a Silly-Putty-like material, the team used a twin-screw extruder, which is as damaging as it sounds. The machine bores two screws into a material and pulls the material through it, destroying some of the material's molecular bonds. Here too, the synthetic material formed more new bonds than those destroyed, becoming much more solid in structure and stronger.

Craig said one drawback to the is that forces deform the material's initial structure. It is stronger at the end, but is not the same shape. The team now plans to create synthetic materials that can repair themselves after stress and retain their original shape, he said.

The team would also like to engineer the material to respond faster. "At this point it takes minutes for the strengthening reactions to start changing the material," Craig said. "We could see it happening as quickly as milliseconds."

Explore further: Playing with glass safely—and making it stronger

More information: "Mechanochemical Strengthening of a Synthetic Polymer in Response to Typically Destructive Shear Forces," Black Ramirez, A. et. al. Nature Chemistry, August 2013. DOI: 10.1038/nchem.1720

Related Stories

'Molecular levers' may make materials better

Dec 23, 2012

(Phys.org)—In a forced game of molecular tug-of war, some strings of atoms can act like a lever, accelerating reactions 1000 times faster than other molecules. The discovery suggests that scientists could ...

Playing with glass safely—and making it stronger

Jul 18, 2013

(Phys.org) —Researchers at Yale have developed a way to alter the microanatomy of glass and measure how the changes affect the material's overall character—offering new possibilities for tailoring glass ...

Researchers unravel secrets of mussels' clinginess

Jul 23, 2013

Unlike barnacles, which cement themselves tightly to the surfaces of rocks, piers or ships, the clamlike bivalves called mussels dangle more loosely from these surfaces, attached by a collection of fine filaments ...

Recommended for you

A greener source of polyester—cork trees

Apr 16, 2014

On the scale of earth-friendly materials, you'd be hard pressed to find two that are farther apart than polyester (not at all) and cork (very). In an unexpected twist, however, scientists are figuring out ...

User comments : 1

Adjust slider to filter visible comments by rank

Display comments: newest first

NikFromNYC
2 / 5 (4) Aug 04, 2013
"It is the first time scientists have used force-induced chemistry within a material to make it stronger in response to stress."

Contrast and compare to work hardening: http://en.m.wikip...ardening

More news stories

NASA's space station Robonaut finally getting legs

Robonaut, the first out-of-this-world humanoid, is finally getting its space legs. For three years, Robonaut has had to manage from the waist up. This new pair of legs means the experimental robot—now stuck ...

Ex-Apple chief plans mobile phone for India

Former Apple chief executive John Sculley, whose marketing skills helped bring the personal computer to desktops worldwide, says he plans to launch a mobile phone in India to exploit its still largely untapped ...

Filipino tests negative for Middle East virus

A Filipino nurse who tested positive for the Middle East virus has been found free of infection in a subsequent examination after he returned home, Philippine health officials said Saturday.

Egypt archaeologists find ancient writer's tomb

Egypt's minister of antiquities says a team of Spanish archaeologists has discovered two tombs in the southern part of the country, one of them belonging to a writer and containing a trove of artifacts including reed pens ...