How the thin film spreads over the recipient's walls in 35 seconds

A novel method for developing conductive and transparent thin films, that could be used in applications ranging from solar cells to ultracapacitors, has been discovered by a team of UCLA researchers, by mistake.

While Julio M. D’Arcy, senior graduate student in Richard B. Kaner’s UCLA lab, was purifying some nanofibers with chloroform in a water container, he observed a thin film of polymer spreading up the walls of the container.

Conducting plastics such as the one discovered by D’Arcy have been touted for a long time, but their wide use had been halted by the difficulties they posed in the process of layering them into films. “Conducting polymers have enormous potential in electronics, and because this technique works with so many substrates, it can be used in a broad spectrum of applications, including organic solar cells, light-emitting diodes, smart glass and sensors,” said Yang Yang, a professor of materials science and engineering at the Samueli School of Engineering and Applied Science and faculty director of the Nano Renewable Energy Center at the CNSI.

A Physorg article mentions how the process of creation worked:

When water and oil are mixed, a blend of droplets is formed, creating a water-oil interface that serves as an entry point for trapping polymer nanofibers at liquid-liquid interfaces. As droplets unite, a change in the concentration of blended solids at the water-oil interface leads to a difference in surface tension. Spreading up a glass wall occurs as result of an attempt to reduce the surface-tension difference. Directional fluid flow leads to a continuously conductive thin film comprised of a single monolayer of polymer nanofibers. The uniformity of the film surface is due to the particles being drawn out of the water-oil interface, sandwiched between two fluids of opposing surface tensions.

In the solar cell industry, for example, conductive transparent thin films could be used in making materials with adjustable tint and in organic solar cells. The team wants to increase the number of applications the film could have by also studying other nanomaterials (than carbon nanofibers) with the technique.

What’s mostly attractive about UCLA’s technology is that the thin film can be grown in a matter of seconds at room temperature, from inexpensive and recyclable materials. And it works on any substrate.

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