It's a Bumpy Ride for Nanocars in Air

Subjecting nanocars to ambient conditions offers insights into producing molecular machines

Molecules that alight on a surface used to test nanocars look more like obstacles, according to researchers at Rice University and North Carolina State University testing the mobility of single-molecule cars in open air.
Illustration: Rice University and North Carolina State University
Molecules that alight on a surface used to test nanocars look more like obstacles, according to researchers at Rice University and North Carolina State University testing the mobility of single-molecule cars in open air.
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So-called “nanocars” have been a fixture on the nanotechnology landscape for at least the last decade.  And, no, these will not be cars that we humans will be shrunk down to fit into like in the sixties sci-fi movie “Fantastic Voyage.”  Instead nanocars are molecular-scale devices that can be directed to move around with light or other means and ferry around payloads not unlike the way a macroscale vehicle might.

Now researchers at Rice University, who developed the first nanocars, have teamed up with researchers at North Carolina State University to make it possible for nanocars to move around in ambient environments instead of being restricted to vacuums.

“Our long-term goal is to make nanomachines that operate in ambient environments,” said James Tour of Rice University in a press release. “That’s when they will show potential to become useful tools for medicine and bottom-up manufacturing.”

In research described in the Journal of Physical Chemistry C, progress towards nanocars that can move about outside of a vacuum starts with adamantine wheels that are water repellent (hydrophobic).

Hydrophobicity is key to keeping the nanocars connected to the surface because it minimizes the amount of surface area that comes in contact with the wet surface. If the wheels are attracted to water, they could be swept away in the flow of water. Balance is the key. If the wheels are made too hydrophobic they could be stuck in place.

When it comes to nanocars, the roads they travel on are usually made of glass, or glass coated with the polymer polyethylene glycol (PEG). In the research, a plain glass surface was coated with hydrogen peroxide so the wheels wouldn’t stick and the PEG-coated glass offered a non-sticky surface without any further treatment.

So, it was off to the races. This time the nanocars would be moving on the glass surface exposed to open air rather than in a vacuum. The results were not aimed at achieving the fastest lap times, but to determine the kinetics of nanocar movement and the interaction between the car and the surface over time.

“We want to know what makes a nanocar ‘hit the brakes’ and how much external energy we need to apply to start it moving again,” said Tour in the release.

It was a tough day out on the track. The nanocars, which are really nothing more than molecules made up of a few hundred atoms, had a hard time moving on the glass surfaces that continued to get “dirtier” being exposed to the molecules in the air.  Each one of the molecules acted like a huge obstacle that made it impossible for the nanocars to continue moving.

All the nanocars moved faster on the PEG-coated slides and twice as many nanocars moved on these slides than did on the glass only slides.

While it may have been a tough day for the nanocars, the results are not expected to impact their chances at the upcoming first ever Nanocars Race in France this autumn. The video below offers a little insight into the competition.

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IEEE Spectrum’s nanotechnology blog, featuring news and analysis about the development, applications, and future of science and technology at the nanoscale.