Getting slick on friction

Unless you’re under really powerful medications, you’ve never really thought about water and how weird it is. The lads at The Nexus can tell you all about it (about water, not powerful medications…I don’t think). Mostly because of how every single molecule behaves around each other, they can do things like float as a solid on top of its own liquid because it’s less dense as ice than as water. Also, thanks to that same interaction, this will hurt:

640px-flickr_-_official_u-s-_navy_imagery_-_a_republic_of_korea_navy_sailor_competes_in_the_belly-flop_contest
Wikimedia Commons (Public Domain, Author: Jumar T. Balacy, United States Navy)

Some new research out of the University of Akron is going to add something to that list: liquid water in a tight space under some pressure becomes more slippery.

Wait, what? Water’s slippery enough as it is! We’ve slipped on a wet floor before (yeah, I’m not the only one, don’t judge me), and we’ve seen these around:

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Wikimedia Commons (CC-BY-SA-20 Austria, Author: Otto Normalverbraucher)

…so how can water become even more slippery!? Well, there’s a couple of things we need to get out of the way first, the most important one being friction, which acts against two things (like two molecules, your car and the road, and so on) sliding against each other. The higher the coefficient of friction (‘COF’), the harder it is to slide two surfaces on one another. This is why this famous scene (VIEWER WARNING: Tom Cruise in his underwear) from Risky Business (1983) could only be done on a highly-polished floor (which would have a low COF) and not, say, carpet (which would have a rather high COF). If you could do that on the carpet at your place, then it’s been trampled down to the point of being flat and covered in I don’t know what. That or your socks are covered in oil. Either way, you’re gross.

According to the authors, a thin film of water (which has a rather low COF) isn’t as slick as ice, which has a very low COF. Those of us in the Northern Hemisphere will come face-to-face (hopefully not literally) with this fact yet again soon.

giphy
Auhor unknown

The thing is that the authors found out that the way in which liquid water molecules can come together can lower its COF to where it acts like ice while it’s a thin film in between layers of surfactants, so there’s the next thing I wanted to talk about. A surfactant attaches to surfaces, like soaps on gunk, to create a new surface that repels water. This explains why a wet shower stall may be slippery, but a soapy shower stall is definitely slippery. Snowboarders know all about this. This study, then, gives us some idea of how things slip and slide in a highly-aquatic environment, like the inside of your body or in between cells – you’ve got cells and proteins that are literally gliding along each other on ice-like liquid water.

Inevitably, we have to ask: and we care why!?

This is the time of year when Nobel Prizes are awarded, and the winners for chemistry this year – Sauvage, Stoddart, and Feringa – received it for their work on nanomachines. Unlike what most people think of them (which comes from sci-fi, but nothing wrong with that), these are not tiny robots. Instead, these ‘machines’ are nothing more than molecules using chemical reactions and molecular interactions (think of the things that happen when you get two magnets together – you’re getting the idea) in order to move, open up, close up, and so on. There’s your nano-scale right there. The more we know about the kind of environments that these nanomachines will be working in, the better we can develop nanomachines that can do some really neat things like deliver meds directly into cells, maybe even sneak into cancerous tumor cells and sabotage them. Real special-ops stuff at the molecular level – perhaps knowledge of this will help insert our nano-agents into the hot zone.

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Wikimedia Commons (Public Domain, Author: SSgt. Samuel Morse, United States Air Force)

That’s it – no more Call of Duty before bed.

Featured Article: Dhopatkar N, Defante AP, Dhinojwala A (2016). Ice-like water supports hydration forces and eases sliding friction. Science Advances. doi: 10.1126/sciadv.1600763)

Featured Image: Wikimedia Commons/Flickr (CC-BY-SA-20, author: Marshall Astor)

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7 Comments

  1. As always, a wonderful post. And personally, I’m not sure there’s ever an incorrect time for Call of Duty…but then again I lived off that game for a few months once. The carpet was quite flat where I sat — no oily socks, though!

    Liked by 1 person

      1. Get them to play the zombie mode — you can chuck all the grenades you want and you can’t hurt your teammates. Good stress relief AND you get to keep your friends!

        Like

      1. That is good advice! I am heading into the teaching field, not high school so I won’t have to worry about putting anyone to sleep. Though community college might be just as big of an issue! But by then it’s not my fault they are paying to see me! HA!

        Like

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