Researchers create flexible and flexible materials with improved properties

A team of polymer chemists and engineers from Carnegie Mellon University has developed a new methodology that can be used to create a class of stretch polymer composites with improved electrical and thermal properties. These materials are promising candidates for use in soft robotics, auto-healing electronics and medical devices. The results are published in the May 20 issue of Nature Nanotechnology.

In this study, researchers combined their expertise in basic science and engineering to develop a method that consistently incorporated eutectic gallium indium (EGaIn), a liquid metal alloy at room temperature, into an elastomer. This created a new material: a multifunctional composite that is highly extensible, flexible, with a high level of thermal stability and electrical conductivity.

Carmel Majidi, professor of mechanical engineering at Carnegie Mellon and director of the Soft Machines Lab, has conducted extensive research on the development of new flexible materials that can be used in biomedical or other applications. As part of his research, he has developed rubber composites containing nanoscopic droplets of liquid metal. The materials looked promising, but the mechanical mixing technique he used to combine the components resulted in materials with inconsistent composition and therefore inconsistent properties.

To overcome this problem, Majidi spoke to polymer chemist Carnegie Mellon and JC Warner University Professor of Natural Sciences Krzysztof Matyjaszewski, who developed Radical Atom Transfer Polymerization (ATRP) in 1994. ATRP, the first and most robust method of controlled polymerization, allows scientists to chain monomers piece by piece, resulting in highly tailored polymers with specific properties.

"New materials are only as effective as they are reliable, you should know that your equipment will work the same way every time before you can make it a commercial product," Matyjaszewski said. "ATRP has proven to be a powerful tool for creating new materials with consistent, reliable structures and unique properties."

Majidi, Matyjaszewski and Michael R. Bockstaller, Professor of Materials Science and Engineering, used ATRP to attach monomer brushes to the surface of EGaIn nanodroplets. The brushes were able to bond to each other and form strong bonds with the droplets. As a result, the liquid metal disperses evenly throughout the elastomer resulting in a material having high elasticity and high thermal conductivity.

Matyjaszewski also noted that after polymer grafting, eGaIn's crystallization temperature had been lowered from 15 ° C to -80 ° C, thus prolonging the liquid phase of the droplet – and thus its liquid properties – to # 39 at very low temperatures.

"We can now suspend the liquid metal in virtually all polymers and copolymers in order to adapt their material properties and improve their performance," Majidi said. "This has not been done before, which opens the door to the discovery of new materials."

The researchers plan to use this process to combine different polymers with a liquid metal and, by controlling the concentration of liquid metal, to control the properties of the materials that they create. The number of possible combinations is vast, but researchers believe that with the help of artificial intelligence, their approach could be used to design custom-made elastomeric composites with suitable properties. The result will be a new class of materials that can be used in a variety of applications, including soft robotics, artificial skin and biocompatible medical devices.