Something strange happens when you expose ice to an electrical field

Illustration for article titled Something strange happens when you expose ice to an electrical field

A weird thing happens when ice freezes under the influence of an electric field. It turns out that electricity can make water strangely attractive. Yes, that was a pun. Proceed with caution.


One of the fun things about science is the many times you scoff at something being impossible, like say, lasers being able to erase metal from x-ray scans, and end up being a fool who was completely wrong about everything. A student in the UK wrote in to a physics site, asking if, since water molecules had a positive and negative side, it could be frozen into a magnet. Scoff, scoff, I thought. When water freezes, its molecules shift into a rigid lattice. Nothing like that could ever happen. Scoff.

Yes, stupid me, it can. No, water can't form what we'd call a magnet, even when freezing under a magnetic field. It can't attract metal. It can, however, exert an undeniable attraction on tumble-dried clothes because instead of a magnetic dipole it forms an electric dipole. This means that, for example, it can swoop up things like balloons that have been rubbed against hair, and other (extremely light) things that are generally used in static electricity demonstrations.

Illustration for article titled Something strange happens when you expose ice to an electrical field

I would never have believed that anything like this could happen. That it can is because of the weird structure of water. One oxygen and two hydrogen atoms go into making every water molecule. The arrangement they make looks a bit like a round oxygen molecule walking along on two stubby hydrogen legs. They're stuck together with their combined electrons in between them, but the oxygen grabs the electrons tight to itself, leaving its hydrogen molecules facing the outside world with their protons exposed (the cad!). The electrons near the oxygen side make that part of the molecule slightly negative, while the end with the hydrogen protons takes its exposure well and is kicking along quite positively. When one water molecule encounters another, the negative oxygen side of one will be attracted to the positive hydrogen side of the other, and they'll cling together, briefly, before another force acts on them and breaks them apart. This clinging, called a hydrogen bond, is why water is liquid (at room temperature) to begin with. All those quickie hydrogen bonds make it cling together, but also give way to other forces.

In ice, the hydrogen bonds force themselves to be spaced a little farther apart than they are in liquid water, which is why water expands and ice floats. It's that regular spacing that made me think that ice couldn't form any kind of dipole. What a fool I was! In an electric field, water molecules align themselves so that their positive ends face one way and their negative ends face the other. That directional quality can actually stay in the water as it freezes, so a frozen icicle can have one end with only the positive hydrogen ends of the water sticking outwards and one end with only the negative oxygen ends sticking outwards. The difference between this and the rubbed balloon or plastic rod or staticky sock? They have an abundance of one charge or the other. The balloon, for example, is negative all over. The rod, though has a positive end and a negative end. It's a dipole. So it should be able to attract anything with an overabundance of one charge or another - provided its light enough.


Top Image: Wing-Chi Poon

Second Image: Wiki Commons

Via Physics Central and Edinformatics.




F*cking water - how does it work?