Science in a Cuppa.

I implied in the last post that I'm a tea addict. I'm not really, that was all just part of the narrative. I am an Englishman though, and as such, it's in my genes to love a good cuppa. A nice brew. A 3-bag pot. Tea, tea, tea. I don't think there are many countries that drink it quite like we do - and no, I don't think Asian green and herbal tea drinkers count. I'm talking about a cup of the black stuff with a little splash of milk. Only the Irish beat us at constant tea drinking, but they beat us at everything, from being able to hold their alcohol, to uncomprimising religious zealotry. It is only because I know they also beat us at having a sense of humour that I think I'll get away with that remark.

It should be no surprise then that, when an Englishman ends up with a career in science, said Englishman may end up revolving their experiments, theories and understanding of the world around the good stuff. Let's have a look at a couple of examples where having a cuppa tea (or coffee, if you insist) has impacted science...

1. Quantum mechanics. Take your 10:45 pot of tea, and do the unthinkable: pour some into a polystyrene cup. Add some milk (this really should go first, but only if you're an expert tea-smith) and then find a goldilocks surface that's not too smooth and not too rough (treated wood works), and drag the cup along the surface. If you get the speed and friction just right, you may see a little droplet appear on the tea that scuttles along the surface vibrations. How this works is a little subtle, but essentially, the vibrating surface bounces the drop faster than the air between the drop and liquid can escape. The air acts like a cushion, and because it can't escape fast enough, the two liquids never directly contact, and never merge. Why is this important? The pilot-wave idea. This is a fantastic analogy of one of modern physics's attempts to explain one of the stranger aspects of the microscopic: wave-particle duality. It seems that, depending on the circumstances, light, for example, can behave either like a little packet of energy and momentum (a particle), or a ripple in an electromagnetic field (a wave). Can it really be both a wave and a particle? Well, de Broglie long ago suggested an alternative model. He suggested that light is in fact a particle riding on its own vibration in space. It's a particle, which creates a wave, which moves the particle. Not making sense? I'm not surprised. Hopefully the video will help. It's possible to do this with water, but who wants to sit around with a cup of water? No one, that's who.

A home made coffee stain. I did it for science. I did it because I'm clumsy.

2. Ink-jet printing. Hey, it's not all abstract science here, industry gets a shout too. One of the obstacles to high precision printing, particularly if you want to print cheap nanodevices, is something called the coffee-ring effect. If it'd been up to me it would have been called the tea-ring effect, but hey-ho. When coffee (or tea) is spilt, it starts off as a nice uniformly coloured wet patch, but wait an hour, and it won't be so uniform any more, most of the dissolved stuff will be deposited at the edges. All the little coffee or tea particulates are swept to the edge as the drop evaporates. The reason for this usually requires diagrams, but essentially, if you looked at a drop from the side you'd see that it shrinks downwards and not inwards - because it's pinned. On a microscopic scale though it is evaporating from all over the surface. So, to maintain a smooth surface (because that's what liquids do) any water molecules lost to evaporation from the edges must be replenished by a flow from the middle of the drop. This flow is what drags all those tasty particulates to the edge, and what you're left with is a ring-stain. This may seem trivial, but it's a big problem if you want to use ink-jet printing to cheaply print uniform devices, and not just a load of rings. There is a wealth of research into overcoming this problem, which is lucky for me, as it enabled me to get a doctorate in watching things dry.

3. Anti-gravity tea leaves. Fill your cup of green tea with water, let it sit for a bit, and then slowly pour more water into that. What a couple of scientists in Cuba noticed was that some of the leaves will float upwards against the stream, like little leafy salmon fighting the waterfall - but presumably without the furious egg laying at the top. There seems to be some contention as to what causes this upward flow, which this wiki article sums up nicely. The original authors suggested a surface tension gradient was to blame (I'm skeptical), but with collaboration they've since also suggested that eddies in the flow are a likely culprit. Maybe I should ask a kayaking friend if an eddie has ever dragged them upstream. Will report back. 

A bird, mid-flight, spilling water everywhere, demonstrating the teapot effect.

A bird, mid-flight, spilling water everywhere, demonstrating the teapot effect.

4. Hydrophobicity. I've had good teapots and bad teapots in my time, and the bad ones were distinguishable by one key feature - they always spilled. Most of the tea poured out the nozzle fine, but a small amount would dribble down its side and onto the table. Turns out this has got a name, the Teapot effect. A group of French scientists in 2009 examined this in depth, and showed that, if you make the nozzle hydrophobic (water repellant), it won't dribble. This seemed obvious to me, but to a pottery maker not so familiar with concepts of hydrophobicity it might not be. Water, like every fluid, "likes" being on some surfaces more than others (it's not alive, so really it doesn't like anything, but things spread when the free energy of the system is reduced by a large contact area). On metals for example, water will spread, but on greasy or fatty surfaces, water will be repelled and bead up. You can get water repellancy chemically, Teflon being a good example of a chemically hydrophobic material. You can also do it physically, such as in the case of the Lotus Leaf, where tiny hairs hold the drop aloft and the drop remains almost spherical. Life, as ever, finds the simplest solution. Water repellency would be a useful property for windows (imagine no water marks after a rainy day), and in a whole host of other industrial applications. These French scientists though ruined the ride by suggesting we spread butter on the end of the teapot to achieve hydrophobicity. Butter on a teapot! Unbelievable.

5. Sloshing Dynamics. Walk 10 paces with a cup of tea with your eyes closed, and you're almost definitely going to spill it. This isn't just common sense, scientists showed mathematically that the oscillations caused by walking will set up an unstable wave in the surface of a cup of tea (well, coffee, but they would because they're American). What does this mean? It means you'll get a wave, that turns into a slosh, that turns into a spill, that turns into a 1st degree burn. Why is this important? Well, sloshing fluids have been implicated in several rocket anomalies and near catastrophes, so understanding sloshing dynamics is fairly important. The fluid in the case of the misbehaving rocket was the propellant, but I suspect a NASA scientist with a coffee-scalded hand could have been equally dangerous to a mission.

6. Tea itself. This is a bit of a cop-out, but when the Royal Society of Chemistry makes an announcement about how to prepare the perfect brew, we learn a lot about the mind of a scientist. This hilarious Guardian article goes through the RSCs recommended steps... But then the author changes their mind at the end and suggests we do as we please. While I can see that tea is highly personal, this slapdash approach to life is a road to madness. So what were the RSC's recommendations? 

  • Use a tea pot. The teabag shouldn't see the mug. Not ever.
  • Pour the milk into your cup first, and add the brewed tea to that. Wars have been started over less controversial statements than this. The idea is that this way, the milk heats up evenly and doesn't denature.
  • Only brew the tea in just-boiled water and only for around 3 minutes. This releases the caffeine and develops the tannins to just the right level. Too far and it will become astringent, too little and it will taste like bath water. When I asked my Australian chemist friend about tannin chemistry in wine, he looked soberly (ironically, for an Ozzy) off into the distance as if I'd asked something profound. Apparently tannin chemistry is hard. 

And on that note, I really need a cup of tea. I don't have a problem, honest.