Carbon nanotube 'wires' self-assemble in electric field

Introducing 'Teslaphoresis', where a Tesla coil and antenna remotely force powdered carbon nanotubes to assemble into electricity-conducting wires. Belinda Smith reports.

A Tesla coil in action is an impressive piece of hardware, shooting huge cracks of artificial lightning metres through the air. But researchers from the US have shown they're more than museum displays that spit out electric zaps on demand.

By harnessing the power of a Tesla coil, Lindsey Bornhoeft from Texas A&M University and colleagues remotely forced carbon nanotubes to quickly assemble into chains, and even completing a circuit to switch on lights. They reported their technique, dubbed "Teslaphoresis", in the journal ACS Nano.

“Electric fields have been used to move small objects, but only over ultrashort distances,” senior author and Rice University chemist Paul Cherukuri said.

“With Teslaphoresis, we have the ability to massively scale up force fields to move matter remotely.”

Nikola Tesla invented the coil in the late 1800s, and envisioned his invention would deliver wireless electrical energy around the world. But the idea turned out to be impractical – while near-field devices could absorb enough energy to work, the coil's transmission had to be cranked up to power devices further away.

Bornhoeft and her colleagues saw the potential for other uses. As a Tesla coil powers up, it creates an electric field by jiggling electrons in and out of molecules in the surrounding air. This ionisation means the air around the device is charged, and can conduct electricity.

An antenna, placed at the end of a Tesla coil, can coax this electric field into near-parallel lines into space and act as a kind of tractor beam.

To test if these force lines could shift materials, the researchers used powdered carbon nanotubes – single-atom-thick layers of carbon rolled into cylinders.

When they added one milligram of powdered carbon nanotube to liquid and placed the dish eight centimetres in front of the field-focusing antenna, they were amazing to see the powder sprout into a neat line in seconds. (The movement was triggered by the electric field oscillating positive and negative charges of the nanotubes.)

A directed electric field from the Tesla coil causes carbon nanotubes to snap into a wire-like configuration. – Jeff Fitlow

The lines grew quickly too – each end of the nanotube "wire" grew at around two centimetres per second. When all the powder was in line, the whole thing shimmied towards the antenna at around half a centimetre per second.

In one experiment, the researchers formed a circuit between two LEDs. Energy absorbed from the Tesla coil field by the nanotube "wires" then switched the lights on.

The longest line they made using Teslaphoresis was 15 centimetres. And when the researchers turned off the coil, used tweezers to "break" the line, and turned the coil on again, the nanotube "wire" healed itself.

Teslaphoresis' theoretical range is not only dictated by the transmitter's power but also the antenna. This remote control, they write, could be used to make fibres tens of metres long.

They're confident that the process can be scaled up quickly by using multiple Tesla coils to create complex fields and therefore, complex circuits – all without having to touch the nanotubes.

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