Bendy see-thru mobes? Materials scientists make nanofilm advance

The film will be used for rollable and expandable smartphone screens

Researchers have created a new flexible nanomaterial film that boasts a “world record” combination of transparency and electrical conductivity, making it an ideal candidate for roll-up touchscreens.

Transparent nanomaterial films have been used for bendable screens before. Lenovo showcased its CPlus, a flexible phone that can wrap around a wrist, earlier this month.

The new method to make the conductive film was devised by researchers from the University of Illinois at Chicago and Korea University. It uses a technique known as electrospinning and electroplating to weave together a mat of nanofibre, according to new research published in Advanced Materials.

First, polyacrylonitrile, a type of polymer resin, is subjected to a high voltage which causes a droplet to form on the polymer tip. The droplet becomes charged, and the electrostatic repulsion causes the droplet to grow until a stream of resin breaks free from its surface. The stream is caught on a collector which spins out the polyacrylonitrile fibres with a width that is about one-hundredth the diameter of a human hair.

The fibre shoots out like a rapidly coiling noodle, which when deposited onto a surface intersects itself “a million times”, said Alexander Yarin, co-author of the study and professor of mechanical engineering at the University of Illinois at Chicago.

After the electrospinning process, the web of polyacrylonitrile fibres is spatter-coated with a metal that attracts metal ions. A second layer of metal particles is attached to the fibre’s surface through electroplating to give it conductive properties. Copper, gold, nickel, or silver can be used, mainly because of those metals' high electrical conductivity.

The end result is a tangled web of nanowires that resemble chicken wire. "But most of it is holes," Yarin said, which makes it 92 per cent transparent. "You don't see it."

"We can then take the metal-plated fibres and transfer to any surface – the skin of the hand, a leaf, or glass," Yarin said.

The new film is a "world-record combination of high transparency and low electrical resistance," said Sam Yoon, who is also a co-author of the study and a professor of mechanical engineering at Korea University.

By electroplating the fibre junctions, the electrical resistance is lowered, allowing more current to flow and also increases the material’s resiliency,

The film can be bent and stretched repeatedly without changing its properties – an important feature for future touchscreens or wearable technology. ®

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