Weird fluids

Most of us are familiar with the fact that with solid objects, it is harder to start things moving than it is to keep it moving. A similar phenomenon occurs with fluids, where we use the term viscosity to indicate the frictional effects. With most fluids, keeping it stirred is easier or stays the same when compared to starting to stir it.

But there are a few classes of liquids in which the opposite happens and it actually becomes harder to keep stirring once begun. With some, applying pressure or an impact to the fluid can make it seem quite hard. Via Pharyngula, here is video of a demonstration of that effect.

The students in a research lab in the Macromolecular Science department at Case Western Reserve University (where I work) discovered a compound that had such properties. They realized that it would make a good temporary pothole filler. Potholes are the bane of existence in this part of the country where the repeated freeze-thaw cycles in winter are conducive to creating them, and the usual repairs take time to apply (disrupting traffic) and don’t last long.

These students realized that if you put the fluid into waterproof bags, the flexible bags can be simply dropped into the potholes. When cars go over the bags, the impact makes the material hard. Problem solved!


  1. Charles Sullivan says

    As long as they don’t use custard for the pothole bags, because that would attract vermin and make for more roadkill.

  2. katkinkate says

    I have a nit to pick. That yellow stuff in the pool is not custard. It is the makings of custard: cornflour in water at a substantially higher ratio than would be used for making custard, which needs to be boiled until the cornflour is cooked. Although if they boiled the water in that pool, with that much custard powder, the result probably would be stiff enough to walk on if you waited for a nice thick skin to form.

  3. Cera says

    There’s actually an extremely annoying pothole right outside my home that was repaired when I moved in 10 months ago and came back about 3 back.

    So basically what I’m saying is what do I gotta do to get one o’ them bags?

  4. Tyrant al-Kalām says

    Not bad!

    Also I love how they run around in the wilderness wearing lab coats 😀

    They’re doing science all right!

  5. Jared A says

    The media always put us in labcoats when they take our pictures! They make sure the labcoat is white, or how will they know we’re scientists and not mechanics? (Hint: we usually are basically mechanics)

    I was taking part in a educational outreach thing about 18 months ago, and one of the other booths had a demonstration where they unstirred a liquid. That’s right, they put in a drop of food coloring, stirred a bar a about 120 degrees (so that the dye smeared out as the liquid churned). Then they backtracked the stir bar, and all of the dye coalesced back in onto itself into a single droplet. And no, the liquid was not a gel. Totally blew my mind. They told me that there is some dimensionless property that is some ratio of viscosity and container size and a few other things that makes this possible.

  6. ImaginesABeach says

    I know you probably won’t actually see this, because it’s almost a week after the post, but I showed these 2 videos to my Girl Scout troop, and then we spent an hour making non-Newtonian fluids and doing all sorts of fun things while talking about “science in the real world.” Thank you!

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