Monday, February 27, 2012

How a liquid lens works (electrowetting)



A liquid lens works by changing the shape of a water drop by creating an electrostatic field that pulls on the water molecules. I show how water can be affected by a high voltage supply and an electrostatically charged comb.

The process by which the droplet changes shape is known as electrowetting.

6 comments:

Anonymous said...

That's fantastic. I immediately had to try that comb trick. Works a charm. Very cool.

If you're ever short of projects, maybe you could examine something of this nature:
http://virlab.virginia.edu/Nanoscience_class/labs/materials/UVA_super_hydrophobicity_lab_manual.pdf
I don't know about the public availability of the chemicals referenced in this, but the procedures don't look too difficult to this particular laymen's eye.

Anyway, it occurred to me to wonder whether, if you used a sufficiently hydrophobic coating, you could make droplets 'jump' in reaction to the release of a strong electrostatic field.
Judging by the video at this link:
http://www.youtube.com/watch?v=EOF7GpT1YtQ
...it seems like it might be possible--or if not that, perhaps some other neat tricks, perhaps with an array of HV switched electrodes? I don't know, just a wild idea.

Of course that particular procedure is applied directly to a copper surface. I would suppose some additional dielectric coating, both chemically compatible and physically smooth enough, would need to be slipped in the middle somewhere.

Keep the vids coming, Ben, they're awesome. Cheers!

Anonymous said...

Thanks for posting these videos Ben, they're really fantastic!

I just wanted to point out that polar particles are only attracted towards the source of an electric field gradient. In a uniform electric field, both ends of the dipole will feel opposite and equal forces to one another, and so there will be no net force. (Same goes with magnets in magnetic fields). This might be a small point, but I think it is worth considering.

Check out optoelectronic tweezers for an interesting practical application of trapping polarized molecules in electric field gradients. http://nanophotonics.eecs.berkeley.edu/research/oet/oet.htm

Toma┼ż said...

Are you sure it's the polar nature of water that is causing this effect? I'm not very familiar with the physics behind contact angles, but with the running water experiment I'm quite sure the stream of a non-polar liquid would deflect just as well - two plates of a charged capacitor attract each other regardless of the material they are made of.

Nice video though. I love watching your experiments.

Anonymous said...

The polar molecules rotate to align with the field, but they're attracted because the field has a gradient. There's a net force in the direction of increasing field. There would be no net force in a uniform field because the forces on the opposite charges would cancel.

Peter Barvoets said...

is your lens similar to this: http://www.technovelgy.com/ct/Science-Fiction-News.asp?NewsNum=946
I have been interested in water lenses for a number of years. Would love to see a working example

Ben Krasnow said...

Peter, yes that's the same lens. You can search my youtube channel for another video about that specific lens.

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