Tag Archives: physics

Freezing fungal farts: what is hair ice and why does it form?

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Hair ice, in which ice crystals grow in thread-like structures, can be found at northerly latitudes in broadleaf forests [image source]

I’ve written about water before and in particular, if you’ve been paying very close attention, you might remember that November 12th marks the anniversary of the day, in 1783, that Antoine Lavoisier formally declared water to be a compound rather than an element.

Which means that November is always an excellent time to talk about water. But this time, I’m going to focus on its solid state: ice.

A few days ago I stumbled across some beautiful images of hair ice, which prompted me to make a #272sci Twitter post (keep an eye on that hashtag for similar small bits of interesting science). The story behind hair ice is a fascinating one, and not something I could truly cover in 272 characters – so here’s the slightly longer version…

This form of ice is found on dead wood, and it has a few other names, including ice wool or frost beard. Of course, ice naturally forms at 0 ℃ at standard atmospheric pressure, but the form we’re most familiar with looks, to the naked eye at least, rather more random. In fact, it was snowing here just yesterday, which means I have photos!

Ice crystals on a wall in Oxfordshire, UK, in November 2021

As you can (hopefully) see, there’s some regularity to the individual crystals, but they’re sort of growing all over the place. So, how do ice crystals form, and why?

We need to start with the structure of water. Now, you might imagine that a molecule with the formula H2O would have its atoms arranged in a straight line, like this: H–O–H. But it doesn’t, and the reason it doesn’t is that the oxygen atom in the middle has two pairs of electrons which aren’t involved in bonding – which chemists call ‘lone pairs‘.

Imagine, for a moment, that you have a bunch of balloons made up of two sausage-shaped balloons and two round ones, all attached at the neck. What shape would they make, as a whole? Probably, the two long balloons would form a sort of rough V, and the two round ones would stick out, opposite each other.

If you have some balloons to hand, give it a try. It turns out this is actually a pretty good model for water. We end up with a roughly tetrahedral shape, with oxygen in the middle, hydrogen atoms in two of the corners, and the lone pairs in the other two corners.

The H2O atoms in a water molecule adopt a sort of shallow V shape but, if you consider the lone pairs, the molecule actually forms a rough tetrahedron [image source]

This is important because those lone pairs don’t just sit around doing nothing. The element oxygen is very electronegative, which means it likes to attract bonded electrons. Hydrogen, by contrast, is more electropositive, which essentially means it doesn’t.

The result of this is that, although it is very definitely a covalently-bonded molecule (and not made up of ions), the oxygen atom in water has a partially negative charge, while the hydrogens have a partially-positive charge.

Since positive charges attract negative charges, and since molecules don’t exist in isolation. The result is that the hydrogen atoms in one water molecule are attracted to the oxygens in other water molecules. This is called hydrogen bonding.

If your head is spinning as you try to imagine this, take a look at the image below. White is hydrogen, red is oxygen, and the dashed lines represent the attractions between partially-positive hydrogens and partially-negative oxygens.

Do you see the shapes that form? Yes – hexagons!

When water molecules pack together they form hexagonal shapes [image source]

And how many sides does a snowflake have? Yes – six!

It’s not a coincidence: as the temperature drops, molecules that previously had freedom of movement gradually stop moving so much and pack into these hexagonal shapes. Then, water vapour in the air deposits onto this skeleton and, voilà, we end up with six-sided ice crystals.

Now, normally, this happens fairly randomly. Yes, all the snowflakes are hexagonal (and there are images of the different patterns that can form in this graphic from Compound Interest) but, as my photos of ice crystals suggest, they tend to stick out in all directions.

Hair ice is different. The ‘hairs’ appear at what are called wood rays, that is, lines perpendicular to the growth rings of the wood, and it turns out that if a piece of wood forms hair ice once, it will probably keep producing it – which makes things rather easier for the potential photographer!

Each of the hairs is about 0.02 mm thick and, assuming the temperature doesn’t rise above freezing, they can hang around for hours and even days.

Why does hair ice grow in single, curling strands, rather than forming this more typical ‘bushy’ structure?

Which leads to the question: why don’t more ice crystals grow on top of the threads and break up the hair-like structures? After all, if it’s cold enough for ice, it ought to be cold enough for, well, more ice – oughtn’t it?

A quick aside: you’ve probably heard of Alfred Wegener, discoverer of continental drift – an idea that ultimately led to modern tectonic plate theory. These days, those ideas are pretty universally accepted, but when Wegener first proposed continental drift in 1912, he faced a lot of opposition. There was more than one reason for this, but one major one was that Wegener was seen as an outsider to the field of geophysics. His background was in meteorology and polar research. In other words, he spent a lot of time in cold weather conditions.

Which brings me back to the main, ah, thread (sorry). Alfred Wegener described hair ice on wet dead wood in 1918, having observed it the year before, and suggested that mycelium, the thread-like part of a fungal colony, could be involved. He thought this because he could actually see mycelium on the branch surface, which was confirmed by his consultant, Arthur Meyer. Meyer, however, was unable to definitely identify the fungal species at the time.

Some years later, in 1975, scientists named Mühleisen and Lämmle actually managed to grow hair ice on rotten wood in a climate chamber and later still, in 2005, the physicist Gerhart Wagner again suggested that a fungus was involved, although he had no knowledge of Wegener’s observations when he first did so. He went on to carry out experiments with Christian Mätzler in which they were able to reliably grow hair ice on a balcony on nights with freezing conditions.

A photo of hair ice taken in British Columbia, Canada, by Tiarra Friskie

After lots of painstaking (and cold!) observation, they concluded two things: firstly, hair ice forms from water stored in the wood, not atmospheric water – which goes some way to explaining why the structures aren’t more random, as you’d expect if the ice were forming from water vapour in the air.

Secondly, the fungus, as a product of its metabolism, was generating gas pressure, and that was pushing water through the wood rays to the wood surface, where it was fanning out into fine, curling strands.

So, yes, in a way, hair ice is the product of freezing fungal farts. (Yes, yes, very tenuous, but I couldn’t resist ‘freezing fungal farts’, let me have this one.)

There’s a much more scientific explanation in this 2015 paper, the full text of which is freely available online (lots of great photos too!). The culprit turns out to be a fungus called Exidiopsis effusa. Inside the wood, attractions between the water molecules and the wood surface lower the melting point of water slightly, keeping it liquid. Products of wood decomposition left by the fungus also (probably) help to prevent ice forming inside the wood itself.

Once the outside temperature drops, though, the formation of ice crystals on the outer surface of the wood has the effect of drawing out more water, and the result is that the crystals grown in long, thread-like structures – although the fine details of how the fungus does what it does are still a bit of a mystery. Still, it’s nice to find a not-quite-answered science question, isn’t it?

More hair ice in the wild, by Tiarra Friskie

One final thing: just in case you were thinking, oh, come on, is that first picture really real? On the Chronicle Flask Facebook page, a user named Tiarra Friskie commented that they had pictures of this very phenomenon, taken in British Columbia, Canada, and kindly gave me permission to use them. So, here you are: a tiny bit meltier than the picture above, but nevertheless, two guaranteed genuine photographs of hair ice!

If you live somewhere in the vicinity of the latitudes between 45 and 55 °N (which includes most of the UK, by the way), keep an eye out for rotten wood in your local broadleaf forest – if the weather gets cold enough, you might just spot some hair ice yourself.

A little admin note: the chronicle flask blog is now (yikes) almost nine years and 150 posts old. Life is increasingly busy and so, after December 2021, I’m going to stop making monthly updates. But not to worry! You can still follow the Twitter hashtag #272sci for regular tiny pieces of science, and I’ll pop back every now and then. Oh, and please do consider supporting the Great Explanations book project here!

Plus, why not take a look at my fiction blog: the fiction phial? And you can also find me doing various flavours of editor-type-stuff at the horror podcast, PseudoPod.org – so head over there, too!

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Any old ions?

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The other day, thanks to an expedition to the swimming pool, I found myself drying my hair twice in one day. As I did so it occurred to me that the process was a lot faster at home with my old, battered hair dryer that it had been in the pool changing rooms.

I pondered variables (what can I say, I’m a scientist). I hadn’t washed my hair at the pool, I’d just rinsed it (hence the need to wash it again later) which meant no shampoo and, critically, no conditioner. Does conditioner’s presumably slightly hydrophobic nature help your hair to shrug off extra moisture? This didn’t seem like it ought to make that much difference. It seemed much more likely that the difference was simply due to the hair dryer itself.

hair-dryer

My battered old hair dryer.

And this got me thinking about the nature of my much-loved, rather battered, bright red hair dryer.

I’m going to ‘fess up here. I didn’t buy this hair dryer because I’d carefully researched its specifications and features and decided it was the best model for the job. No, if I’m honest I bought it because it was red and all the others were boring black and silver. Rational eh?

However, I do remember something about this particular hair dryer, and you can just about see a reference to this feature on the photo. Namely, it apparently contains an “ionic generator”. The little dial that you can see in the middle of the photo (set to orange, which if I recall correctly means, ‘maximum ions’) apparently adjusts the ion levels.

At the time I did try to find out exactly what the technology might be. I recall it was difficult – there didn’t seem to be much information out there – and since to be honest I didn’t care that much so long as it dried my hair, and it wasn’t particularly expensive (and it was red, RED!) I bought it anyway.

It only takes a quick glance at Amazon to see that the idea has not gone away. There are lots of ‘ionic’ hair dryers on the market, making claims such as, “Ionic conditioning with 90 per cent more ions“, “Heat-balancing ionic technology for condition and shine and a frizz-free finish“, “stylish dryer with ionic technology–seals in moisture to the hair cuticle for increased shine and silky, glossy hair” and the simple “4X More Ions“.

Hm.

Ok, well first of all what are ions? Whereas most people have a faint idea what atoms and molecules are, far fewer are confident to describe ions – despite the fact that they are firmly a part of the compulsory GCSE Science syllabus and were, of course, also included in  O-level Chemistry before that. Exactly why this should be is tricky to explain. Possibly it’s simply because ‘atoms’ and ‘molecules’ do occasionally crop up in everyday speech, whereas ions are that bit more obscure. Possibly it’s because children learn about atoms in the most basic terms quite early on, and come back to the idea regularly, but ions only turn up relatively briefly (unless, of course, you choose to study A-level Chemistry). There may be an element (hoho) of confusion over the fact that element 26 is called ‘iron’, which in most English accents sounds the same as ‘ion’. And just to really confound everyone, there are such things as iron ions.

But I think the most likely is that ions are a bit tricky to understand.

I’ll have a go.

Ions are charged particles.

There, that was easy, wasn’t it?

What do you mean, what does ‘charged’ mean? It means they have either a positive or negative charge.

What do you mean, ‘what does that mean’?

Oh all right. All right. Back to basics.

helium atom

A helium atom containing a tiny nucleus made up of two protons and two neutrons (red and blue), surrounded by an ‘electron cloud’. 1 fm = 0.0000000000010 millimetres.

First of all we need to understand a bit about atoms. Atoms are made up of two parts. There is the nucleus, which is made up of protons and neutrons (except for hydrogen’s nucleus, which is just a proton) and then, whizzing around that, are electrons. Electrons are quite fiddly things that behave frankly very oddly. In particular, they don’t actually drift around atoms in stately orbits as shown in most diagrams. In fact, they are sort of there and sort of not-there at the same time, and chemists talk about an ‘electron cloud’ as a result. An electron cloud need not contain lots of electrons (this depends on the size of the atom) – it just describes an area where you might find one or more electrons.

Anyway, that’s all a bit complicated and for our purposes it doesn’t really matter – all we need to know is that there’s a nucleus in the middle and electrons around it.

Electrons have a negative charge, protons have a positive charge, and neutrons have no charge. It’s quite difficult to rigorously define what I mean by ‘charge’ without getting into some tricky maths and physics. If you are ok with the idea of negative numbers (who hasn’t had an overdraft at some point or another?) then think of it like this: electrons are -1 and protons are +1 (and neutrons are 0). If you have one proton and one electron, the overall ‘balance’ is zero – their charges cancel each other out. In the case of helium, there are two protons and two electrons. This neat bit of balancing is no accident: it’s the case for all atoms. Carbon has 6 protons and 6 electrons. Oxygen has 8 protons and 8 electrons. Calcium has 20 protons and 20 electrons, and so on.

If the electrons and protons aren’t balanced for some reason (usually as a result of a chemical reaction) then the thing that you were calling an atom a moment ago stops being an atom and becomes, wait for it….

An ion!

Oxygen atoms have 8 protons and 8 electrons, but oxygen ions (properly called oxide ions) have 8 protons and 10 electrons. Which means they have a bit more minus than plus. They are, if you like, a bit overdrawn. If you add it up, you find the number works out as -2. And so we say that oxide ions have a charge of -2, and chemists (who are lazy) write this as O2-. Which is not, we must be careful here, the same thing as O2. That means two oxygen atoms joined together, to make an oxygen molecule. What do you mean it’s confusing?

One more example then. Calcium atoms have 20 protons and 20 electrons, but calcium ions have 20 protons and 18 electrons. Add that up and you get +2. We say that calcium ions have a charge of +2, and write Ca2+(and there’s no such thing as Ca2, so that’s one less thing to worry about).

Where have we got to? Ions are charged particles, and that means that they either have a positive charge or a negative charge. These charges are typically between 1 and 3, positive or negative.

mineral water label

Fizzy mineral water, chock full of lovely ions.

Ions are very important, because they form during chemical reactions and many everyday substances are made up of ions. For example table salt, sodium chloride, is made up of Cl– ions and Na+ ions.

Tap water, and indeed bottled water, are full of ions. Tap water has chloride ions (chlorinated water is a jolly good thing, assuming you don’t want typhoid, and is definitely not harmful regardless of what your nearest quack might try and tell you). It might also have fluoride ions, which are also very good for your general health (again, there’s lots of nonsense spread about this). Both tap and mineral water usually contain some sodium ions and some calcium ions. The ion balance does affect the taste – the more sodium there is the more salty the water tastes, for example – but that’s about it really. The ions don’t give the water any special properties except, perhaps, the ability to conduct electricity (which pure water, as in just H2O, actually does really badly).

Having explained ions, let’s get back to hair dryers for a moment. Ionic hair dryers claim to produce streams of negatively-charged ions. They usually claim to use something like the mineral tourmaline to do this, but despite much searching I struggled to find out much about how this was supposed to work or, most crucially, what the negative ions actually are. Negative ions are not a thing in and of themselves. They must be ions formed from atoms, so which element? Or elements?

After much hunting I eventually came upon an interesting piece written by Andrew Alden, at about.com. He explains that tourmaline has an interesting trick called pyroelectricity, which means that it does become charged when heated. The ancient Greeks even knew about this: in 314 BC Theoprastus noticed that tourmaline (called lyngourion at the time) attracted sawdust and bits of straw when heated.

Ed Trollope, from Things We Don’t Know, helpfully explained this pyroelectric effect as follows: the crystal structure of tourmaline becomes polarised (in other words the charges already in the structure become unevenly distributed) if you change its temperature. This results in a voltage across the crystal, which in turn leads to a small current being generated.

But I’m still unclear what the ions, if they exist, actually are. And the problem is that if you search for this, the first umpteen links are all pure and utter nonsense. Tourmaline is a complicated mineral that contains a whole host of different metal ions as well as oxygen, OH– (hydroxide) and fluorine. Does it produce oxide ions, O2-? These are very reactive and wouldn’t hang around for any useful length of time. And if they did they would surely be harmful. Presumably they would cause the production of ozone (definitely not a good thing). Are the manufacturers using the word ‘ions’ when they actually mean ‘electrons’? They are not the same thing of course, but perhaps ‘ions’ seemed like a friendlier word.

Electrons would reduce static in your hair, but then static is short-lived anyway. Would it speed up drying time? None of the explanations I’ve actually seen for this including, most memorably, “The negative ions break down water molecules to one-fifth of their size” (errrr, what?), provide a really satisfactory, scientific explanation as to why it should. Or why it should ‘seal water into the hair’, whatever that means. It is feasible that the reduction of static could help keep the hair strands separate, which might help, but surely brushing or even running your fingers through your hair would have a much bigger effect. What I’m also not clear on is whether the tourmaline in your hair dryer carries on producing streams of ions/electrons indefinitely, or whether it becomes degraded over time. Which you would expect, if the charged particles are coming from the tourmaline itself. Is my battered old hair dryer really doing anything at all anymore, if it ever did?

It’s all very unsatisfactory. My best guess? Ionic hair dryers do reduce static build-up in hair, which would leave it smoother immediately after drying. Conditioner and styling products will also help with this mind you, and will probably have a more significant effect. The rest, I strongly suspect, is pure woo. And my hair dryer dries my hair faster simply because it runs hotter and with a faster airflow than the cheap, basic models in the swimming pool changing rooms.

But if you know better, I’d genuinely love to hear from you.