This photo shows the highly conductive ultrathin film on skin between the two clips. Photo: Sam Yoon/Korea University.
This photo shows the highly conductive ultrathin film on skin between the two clips. Photo: Sam Yoon/Korea University.

An ultrathin film that is both transparent and highly conductive has been produced using a cheap and simple method devised by an international team of nanomaterials researchers from the University of Illinois at Chicago and Korea University.

The film – actually a mat of tangled nanofibers, electroplated to form a ‘self-junctioned copper nano-chicken wire’ – is also bendable and stretchable, offering potential applications in roll-up touchscreen displays, wearable electronics, flexible solar cells and electronic skin. The film is described in a paper in Advanced Materials.

"It's important, but difficult, to make materials that are both transparent and conductive," says Alexander Yarin, professor of mechanical engineering at the University of Illinois at Chicago and one of two corresponding authors of the paper.

The new film establishes a "world-record combination of high transparency and low electrical resistance," with the latter at least 10-fold greater than the previous existing record, said Sam Yoon, professor of mechanical engineering at Korea University and the other corresponding author. The film also retains its properties after repeated cycles of severe stretching or bending, Yarin added – an important property for touchscreens or wearables.

Manufacture of the film begins by electrospinning a nanofiber mat of polyacrylonitrile (PAN), which is made up of fibers that are about one-hundredth the diameter of a human hair. In this process, each fiber shoots out like a rapidly coiling noodle, which when deposited onto a surface intersects itself a million times. "The nanofiber spins out in a spiral cone, but forms fractal loops in flight," Yarin explained. "The loops have loops, so it gets very long and very thin."

The naked PAN mat doesn't conduct, so it must then be electroplated with copper – or silver, nickel or gold. The electrospinning and electroplating are both relatively high-throughput, commercially viable-processes that take only a few seconds each, according to the researchers.

"We can then take the metal-plated fibers and transfer to any surface – the skin of the hand, a leaf or glass," Yarin said. An additional application for the ultrathin film could be as a nano-textured surface that dramatically increases cooling efficiency.

Yoon said that the electroplating process causes "self-fusion" at the fiber junctions, which "dramatically reduced the contact resistance". Yarin noted that the metal-plated junctions facilitated percolation of the electric current – and also accounted for the nanomaterial's physical resiliency. "But most of it is holes," he said, which makes it 92% transparent. "You don't see it."

This story is adapted from material from the University of Illinois at Chicago, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.