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Materials

Super stretchy semiconducting polymers

Nanoconfinement helps conjugated polymers flex their electronic properties

by Matt Davenport
January 9, 2017 | A version of this story appeared in Volume 95, Issue 2

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Credit: Bao Research Group
Semiconducting polymers confined within an elastomer can be used to build stretchy circuits, like this transistor, which stands up to being stretched, poked, and prodded.
This image shows a stretchable semiconductor circuit being stretched by a narrow poker.
Credit: Bao Research Group
Semiconducting polymers confined within an elastomer can be used to build stretchy circuits, like this transistor, which stands up to being stretched, poked, and prodded.

Silicon has enabled science journalists to cover topics that were once written about only by science fiction authors: implantable sensors, wearable smart gadgets, and even electronic skin. But silicon is naturally more rigid than is desirable for devices that ought to bend and stretch like living tissue. Some scientists have thus turned to semiconducting polymers to create such devices, but these materials have struggled to achieve flexibility without compromising electrical performance. An international research team has now created thin polymer films that can stretch up to twice their initial length while still allowing electrical charge to flow at rates comparable to silicon (Science 2017, DOI: 10.1126/science.aah4496). Led by Stanford University’s Zhenan Bao and Jong Won Chung of Samsung Advanced Institute of Technology, the team showed that wearable circuits made with the films can withstand bending, twisting, and even light stabbing. This ductile durability comes from confinement. When mixed with an elastic styrene copolymer, some conjugated polymers separate and confine themselves, forming nanoscopic, fibrous aggregates. This nanoconfinement impedes the semiconducting polymer’s inclination to crystallize and facilitates the movement of electrical charges, resulting in an uncompromising stretchy semiconductor, the team reports.

This illustration shows how semiconducting polymers are confined within an elastic polymer to create wearable, flexible circuits.
Several conjugated polymers—including the thiophene-pyrrole copolymer shown—can confine themselves into fibrous networks within a stretchy styrene-ethylene-butylene matrix (SEBS), enabling researchers to create wearable electronics with siliconlike electronic properties.

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