Here’s a curious finding from the University of Bristol in the UK.

Place a droplet onto an inclined plexiglass sheet and shake it up and down. I know what you’re thinking: even without the shaking the drop should dribble down the plate due to gravity unless it is pinned in place by surface tension. Vertical shaking should loosen the drop’s “grip” on the surface and so enhance the speed at which it dribbles. Right?

Actually, exactly the opposite, say Philippe Brunet and pals.  The drop starts to climb up the plate.

Brunet and friends think the shaking introduces a non-linear effect in the frictional force between the drip and plate because of the way the surface area of the drop in contact with the sheet changes with time. So there is less resistance to its upwards motion than its downward progress.

Interesting, no? And useful too, they say.  Engineers need to know how to move droplets around inside microfluidic devices and this could give them an extra tool to play with.

Ref: arxiv.org/abs/0809.1962: Vibration-induced climbing of drops

This entry was posted on Wednesday, September 17th, 2008 at 12:51 am and is filed under Mean machines, Slimey stuff. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.