A plastic that heals itself

WASHINGTON, D.C. — A scratch on your brand new car can be expensive to fix. A teen has helped to make a new plastic that might do more than protect your bumper: It could make small scratches disappear.

Emily Spencer, 18, helped create a plastic that heals itself under ultraviolet light. The material could be used one day to make everything from scratch-proof eyeglass lenses to the door panels and fenders of your next car.

A senior at Hathaway Brown School in Shaker Heights, Ohio, Emily presented her project at the Intel Science Talent Search. The annual event is run by Society for Science & the Public and sponsored by Intel. It brings 40 high school students here to show off their research and to compete for cash awards of up to $150,000 each.

Emily loves thinking about the materials that make up the objects we use every day. “You can look at something like your phone case, and it’s just an object,” she says. People tend to overlook the materials that go into making such objects, she notes. But “we can improve those things and make them better.”

Working with a graduate student in a nearby lab at Case Western Reserve University in Cleveland, Emily developed a new kind of polymer — a material made of long chains of repeating groups of atoms. It looks like a “really thick sort of yellowish plastic wrap,” but it’s far more than that. When Emily’s plastic is scratched, it can heal itself.

All it needs is a quick burst of ultraviolet (UV) light — a part of the light spectrum that is invisible to the human eye. Place a piece of her plastic, scratched with a razor blade, under a UV lamp. The scratch heals while you watch. The healed plastic is just as strong as the original. 

The plastic also has a feature called shape memory. A flat piece can be heated and twisted into a new shape, such as a spiral. It holds that new shape when the plastic is cool. But heat it again, and the material returns to its original, flat shape.

“It’s sort of like hair,” Emily explains. “If my hair is naturally curly and I iron it straight, it will hold the straight shape. But my hair won’t be straight forever. It will ‘remember’ that it’s curly. It will go back to being curly when it’s exposed to water.” She was part of a team that published details on the design of the new plastic in a scientific journal in 2013.

The plastic is a smart material — one that can change when scientists apply stress, heat or water. The material’s flexibility comes from links between the repeating groups of atoms that make up the polymer. Its healing powers come from atoms of sulfur in the plastic. The sulfur atoms bond to each other to form a disulfide bond, holding the plastic in a particular shape. But under UV light, those sulfurs break apart.

“When the bonds break with the UV light, the material becomes kind of flowy,” Emily explains. “It can flow into cracks and imperfections in the material,” healing scratches. Turn off the UV light, and the sulfurs bond together again. Meanwhile, the scratches are gone.

All those sulfur atoms made a nasty stink in the lab. “The reaction [to make the material] smells like rotten eggs,” the teen notes. “I kept apologizing to people in the lab for the smell.”

Emily would like to be able to apply materials like hers to objects such as cars. “If you had your car coated [with the plastic] and then it got scratched, you could first use the heat to activate the shape memory to bring the pieces closer together,” she notes. “Then you could use the UV light to heal the leftover scratches.” This material, and others like it, might one day make those expensive scratches a thing of the past.

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Power Words

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atom   The basic unit of a chemical element. Atoms are made up of a dense nucleus that contains positively charged protons and neutrally charged neutrons. The nucleus is orbited by a cloud of negatively charged electrons.

bond  (in chemistry) A semi-permanent attachment between atoms — or groups of atoms — in a molecule. It’s formed by an attractive force between the participating atoms. Once bonded, the atoms will work as a unit. To separate the component atoms, energy must be supplied to the molecule as heat or some other type of radiation.

disulfide A pair of sulfur atoms linked together.

Intel Science Talent Search    An annual competition run by Society for Science & the Public and sponsored by Intel. It brings 40 high-achieving high school seniors to Washington, D.C. to show their research projects to the public and to compete for awards.

journal  (in science) A publication in which scientists share their research findings with the public. Some journals publish papers from all fields of science, technology, engineering and math, while others are specific to a single subject. The best journals are peer-reviewed: They send out all submitted articles to outside experts to be read and critiqued. The goal, here, is to prevent the publication of mistakes, fraud or sloppy work.

peer review   (in science) A process in which scientists in a field carefully read and critique the work of their peers before it is published in a scientific journal. Peer review helps to prevent sloppy science and bad mistakes from being published. 

plastic  Any of a series of materials that are easily deformable; or synthetic materials that have been made from polymers (long strings of some building-block molecule) that tend to be lightweight, inexpensive and resistant to degradation.

polymer  Substances whose molecules are made of long chains of repeating groups of atoms. Manufactured polymers include nylon, polyvinyl chloride (better known as PVC) and many types of plastics. Natural polymers include rubber, silk and cellulose (found in plants and used to make paper, for example).

shape memory polymer  A smart material made of long chains of repeating atoms. It has the ability to take a new shape and then return to a former shape when light, heat or some other stimulus is applied.

smart material  Materials designed by researchers to change in a controlled way when triggered by a certain temperature, stress, moisture or other stimulus.

Society for Science and the Public (or SSP)  A nonprofit organization created in 1921 andbased in Washington, D.C. Since its founding, SSP has been not only promoting public engagement in scientific research but also the public understanding of science. It created and continues to run three renowned science competitions: The Intel Science Talent Search (begun in 1942), the Intel International Science and Engineering Fair (initially launched in 1950) and Broadcom MASTERS (created in 2010). SSP also publishes award-winning journalism: in Science News (launched in 1922) and Science News for Students (created in 2003). Those magazines also host a series of blogs (including Eureka! Lab).

stress  (in biology) A factor, such as unusual temperatures, moisture or pollution, that affects the health of a species or ecosystem. (in physics) Pressure or tension exerted on a material object.

ultraviolet  A portion of the light spectrum that is close to violet but invisible to the human eye.