Researchers create material that transforms from soft to hard when exposed to light

Inspired by living things, the unique material is 10 times as durable as natural rubber.
Sade Agard
Structure of artificial hexagonal nanomaterial
Structure of artificial hexagonal nanomaterial

iStock/selimcan 

For the first time, researchers use only light and a catalyst to change properties such as hardness and elasticity in molecules of the same type, according to a new study published October 13 in Science.

Inspired by living things like trees and shellfish, the team created a unique material that is ten times as durable as natural rubber and may lead to more flexible electronics and robots.

The ability to control the physical properties of a material using light as a trigger is potentially transformative

"This is the first material of its type," stated Prof. Zachariah Page, co-author of the study, in a press release. "The ability to control crystallization, and therefore the physical properties of the material, with the application of light is potentially transformative for wearable electronics or actuators in soft robotics."

For a long time, scientists have worked to create synthetic materials that imitate the characteristics of living structures like skin and muscle. Structures in living things effortlessly mix qualities like strength and flexibility. However, when employing a combination of diverse synthetic materials to simulate these properties in the lab, the materials often fail, i.e., disintegrate where the different materials meet.

"Oftentimes, when bringing materials together, particularly if they have very different mechanical properties, they want to come apart," said Page. However, by using light to vary how rigid or elastic the material would be, Page and his colleagues could regulate and modify the structure of a material that resembled plastic.

Remarkably, a harder material developed where the light touched it

In this different strategy, the chemists began with a monomer. Simply put, this single molecule forms larger structures known as polymers by joining with other molecules identical to it, much like the polymer in the most widely used plastic.

After testing a dozen catalysts, they discovered one that produced a 'semicrystalline' polymer that resembled those in synthetic rubber when combined with their monomer and exposed to visible light. Remarkably, a harder material developed where the light had touched it, while the unlit portions kept their malleable, soft characteristics.

The substance was stronger and could be stretched farther than other mixed materials since it was formed of a single material with distinct properties.

The novel procedure is quick, affordable, energy-efficient, and environmentally friendly

The monomer and catalyst are readily available commercially, with the reaction occurring at ambient temperature. Additionally, the experiment's light source was blue LED which is inexpensive.

The researchers claim the reaction uses minimal hazardous waste and takes less than an hour, making the procedure quick, affordable, energy-efficient, and environmentally friendly.

In robotics, it is preferable to use strong and elastic materials to enhance movement and durability

According to the research team, the material may be utilized as a flexible foundation to secure electronic components in medical devices or wearables. In robotics, both strong and elastic materials are preferable for improving movement and durability, so there is potential to utilize the novel material in this industry, too.

To further validate the material's utility, the researchers will next try to create more objects using the substance.

Lead author of the study and doctoral student at UT Austin, Adrian Rylski, stated, "We are looking forward to exploring methods of applying this chemistry towards making 3D objects containing both hard and soft components."

Abstract:

An organized combination of stiff and elastic domains within a single material can synergistically tailor bulk mechanical properties. However, synthetic methods to achieve such sophisticated architectures remain elusive. We report a rapid, facile, and environmentally benign method to pattern strong and stiff semicrystalline phases within soft and elastic matrices using stereo-controlled ring-opening metathesis polymerization of an industrial monomer, cis-cyclooctene. Dual polymerization catalysis dictates polyolefin backbone chemistry, which enables patterning of compositionally uniform materials with seamless stiff and elastic interfaces. Visible light–induced activation of a metathesis catalyst results in the formation of semicrystalline trans polyoctenamer rubber, outcompeting the formation of cis polyoctenamer rubber, which occurs at room temperature. This bottom-up approach provides a method for manufacturing polymeric materials with promising applications in soft optoelectronics and robotics.

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