Watch this space for the chemistry of dust


It’s not often that chemists get new tools with which to investigate the building blocks of the world around us, so  a paper on the arXiv today gives them good reason to pop a few corks.

Vladlen Shvedov at the Australian National University in Canberra and a few mates have today unveiled a way of confining and steering aerosol particles in a beam of light.

That hasn’t been possible until now because aerosols are slippery blighters. They absorb huge amounts of light that increases their temperature making them hard to hang on to.

That makes the conventional  way of handling small particles using optical tweezers more or less useless. Optical tweezers rely on radiation pressure to push their charges around. But this is dwarfed by thermal forces and so only works for particles that are relatively cool.

Thermal heating makes particles misbehave because  nonuniform heating makes one side of a particle hotter than the other, causing gas molecules on either side to bounce off with different velecities. This generates a force known as photophoresis.

What Shvedov and his cobbers have done is exploit the photophoretic force to trap partices using  two light beams in the shape of doughnuts.

The result is a device that can trap aerosol particles up to 10 micrometres across  and steer them along trajectories several millimetres long at a rate of around a centmetre per second.

All of a sudden that makes possible a whole host of experiments that were previosuly impossible: developing ecologically clean and safe nanotechnologies, modeleling the chemical proceses at work in the atmosphere and best of all (IMO) simulating interstellar dust .

If you see any chemists with smiles on their faces, you’ll know why. In the meantime look out for some fascinating insights into the chemistry of dust.

Ref: Optical Guiding of Absorbing Nanoclusters in Air

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