22 May 2010 | NewScientist | 21

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How leaves stay frost-freeAS TEMPERATURES plummet, lotus

leaves can remain surprisingly free of

frost. Their secret, which turns out to

be related to their water-repelling

properties, could be applied to

building frost-repelling materials.

Water droplets roll off lotus leaves

partly because of the roughness

of their surface on the nanoscale.

The irregularities trap air beneath

any water droplets on the surface,

preventing them from making contact.

Artificial surfaces with similar

properties are equally water-repellent,

and also resist frost formation.

Now Yanlin Song and his team at

the Chinese Academy of Sciences,

Beijing, have shown that this frost

repellency arises because water

droplets with only a tenuous hold on

a sub-zero surface cannot lose heat to

it, and so are slow to freeze.

The team chilled two chunks of

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Super-magnifying lens created

polypropylene – one with a lotus-leaf-

like “superhydrophobic” surface and

the second a hydrophobic one with

less surface relief. In a humid

atmosphere, spherical water droplets

5 micrometres across condensed on

both surfaces, but as the droplets

grew, those on the hydrophobic

surface flattened out, increasing the

contact area between the droplet

and the surface. These droplets froze

within 90 seconds. Droplets on the

superhydrophobic surface remained

spherical even when they had grown

to 80 micrometres across and only

froze after 6 minutes (Soft Matter,

DOI: 10.1039/c0sm00024h).

Hacking into cars’ electronic controls

–Smooth surfaces freeze faster–

per cent of the world’s computers are running unlicensed software, according to IT analyst group IDC

43

The damage wrought by the collapse of the Deepwater Horizon oil rig should not be allowed to derail offshore drilling, argues Tony Hayward, chief executive of BP, which was using the rig at the time of the accident (Timesonline.co.uk, 14 May)

“Apollo 13 did not stop the space programme”

“Droplets with only a tenuous hold on a sub-zero surface cannot lose heat to the surface”