PHYSICAL CHEMISTRY

Raindrops and Roses

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Science  25 Apr 2003:
Vol. 300, Issue 5619, pp. 551-553
DOI: 10.1126/science.300.5619.551e

It might seem that every small object imaginable has been levitated in a laser trap, and liquid droplets are one of the favorite things that have been used. Since 1975, when Ashkin and Dziedzic trapped a glycerol droplet, a variety of viscous liquid droplets have been captured, although with fairly low efficiencies (below 10%). Water droplets, however, have been difficult to control in this fashion, yet this capability would be extremely valuable for the study of the formation of water droplets and reactions within them. Magome et al. decided not to try to extract a water droplet from the liquid phase, but to grow one in the gas phase instead. They placed an ammonium chloride nucleation center in an infrared laser beam, and water droplets grew from supersaturated vapor to a diameter of 11 m before falling out of the trap; with a 5-mW laser, the efficiency was 46%.—PDS

J. Phys. Chem. B 10.1021/jp034336h (2003).

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