Hairy materials grown on microscale

Materials constructed of tiny little hairs self-assembled at the microscale could be used in the next generation of batteries and solar cells.

The key ingredient is epoxy and when added to a hardener and solvent inside an electric cell and an alternating current applied, the concoction springs into long twisting fibres.

“The process is very simple, the materials are cheap and available and they can grow on almost every surface we’ve tried,” said physicist Igor Aronson from the US Department of Energy’s Argonne National Laboratory.

By tweaking the process, fibres with different shapes can be grown – a short forest of straight, dense hairs; long branching strands; or mushrooms with tiny pearls at the tip – and although the structures can be permanent, the process is also reversible.

“This is a completely new kind of structure,” said Alexey Snezhko. “With this method, you can support more complex structures that have unique properties.”

Argonne materials scientists announced a new technique to grow these little forests at the microscale (the scale shows 100 micrometers, which is about the diameter of a single human hair). Credit: Image by Alexey Snezhko and Igor Aronson, Argonne National Laboratory.

Argonne materials scientists announced a new technique to grow these little forests at the microscale (the scale shows 100 micrometers, which is about the diameter of a single human hair). Credit: Alexey Snezhko and Igor Aronson, Argonne National Laboratory.

The method – published in Nature Communications – offers an alternative to lithography, which is hard to control and yields non-uniform results.

“These polymers assemble themselves, which is much easier and less labour-intensive than lithography,” said Snezhko.

These hairy materials could be used for batteries, photovoltaic cells or sensors thanks to their large surface area. In a proof-of-concept experiment, the team used atomic layer deposition to place a molecule-thick layer of a semiconductor material over the entire hairy structure. This illustrates that the polymer could be used in semiconductor-based renewable energy technologies. It also proved that it could survive temperatures up to 150°C; important if it is to be used in manufacturing.

These micro-sized hairs can also give the surface a superhydrophobic property, or create a surface repellent to dust.

Self-assembled tunable networks of sticky colloidal particles

These tiny “hairs” assemble themselves almost instantly when scientists apply an alternating electrical current. The entire field of view is smaller than the thickness of a credit card. Argonne National Laboratory scientists Alexey Snezhko and Igor Aronson developed this technique, which can grow all kinds of shapes with different tweaks. The “hairy” materials could be useful in next-generation energy technologies, like new and better kinds of batteries.

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