A Question for our local scientists...

So I've run into something that I wanted to know more about. I've recently been making some holiday ornaments from Sculpey an oven bake-able polymer clay. I have some parts that needed sanding, and the accumulated dust was getting a bit bothersome, so I brought a bowl of water in so I could wash my hands when it built up. After washing one time, a drop of the water landed on some of the dust on the sandpaper and formed into a nice small sphere, coated in the dust. It rolls around quite ably, and acts like a solid. Bisecting it with a knife makes two spheres. Squishing it with my finger causes it to act like regular water, its spherical form permanently destroyed.

So what the hell is going on here? :bulb:

Clays are weird. Like really weird. They have extremely unique mechanical properties, and can form very interesting colloids when suspended in water. I'd have to have more time and a chance to look up the specifics of the clay you used, but that's probably what's going on.

Isn't it just the fine dust held to the water with surface tension? You can do the same with talcum powder.

I'm thinking either a(n) ionic/zwitterionic/polar end of the clay polymer interacting with water. You may be familar with anionic surfactants? The polymer is probably of that type, one end is hydrophobic and the other hydrophilic, The -phillic ends sticks in the water surface and other -phobic end sticks out. The droplet gets encased in polymer so it can roll around free from 'sticking'/being wet. It's spherical due to smallest volume/surface area ratio, surface tension of the water etc n 'all that.

If you were to sprinkle the dust in water the opposite would happen. The -phobic ends would gorup up and all point into the center of a spherical mass of polymer, the -phillic ends stick out into the water, forming wiggin's colloids.

I think if you put water on a hydrophobic material you almost always get spherical drops. The thing is that water drops are usually spheres.

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Originally Posted by icks

I'm thinking either a(n) ionic/zwitterionic/polar end of the clay polymer interacting with water. You may be familar with anionic surfactants? The polymer is probably of that type, one end is hydrophobic and the other hydrophilic, The -phillic ends sticks in the water surface and other -phobic end sticks out. The droplet gets encased in polymer so it can roll around free from 'sticking'/being wet. It's spherical due to smallest volume/surface area ratio, surface tension of the water etc n 'all that.

If you were to sprinkle the dust in water the opposite would happen. The -phobic ends would gorup up and all point into the center of a spherical mass of polymer, the -phillic ends stick out into the water, forming wiggin's colloids.

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Clay isn't a polymer. Of course, it's possible there are polymer additives in Illusion's clay (I didn't look it up; still in lab working at an obscene hour, so I don't have time), but I find it unlikely that your proposed phenomenon is what's happening. It depends a lot on the ratio of water to clay, though.

edit: never mind, the product in question isn't clay. It's polyvinyl chloride. Guess we'll have to talk about the fascinating properties of real clay another time.

That's very cool. :up:

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Originally Posted by wiggin

Clay isn't a polymer. Of course, it's possible there are polymer additives in Illusion's clay (I didn't look it up; still in lab working at an obscene hour, so I don't have time), but I find it unlikely that your proposed phenomenon is what's happening. It depends a lot on the ratio of water to clay, though.

edit: never mind, the product in question isn't clay. It's polyvinyl chloride. Guess we'll have to talk about the fascinating properties of real clay another time.

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:)
I was just going off Illusion's post. He siad it was a polymer clay so....

As for real clay, it would be more of a lecture. I don't know much about it, par perhaps it's just an amalgum of minerals.

"Just"? Just?

;)

Funny, I thought the same thing. :D :up:

Honestly, I think clay is one of the most fascinating materials I've ever studied in my coursework (never done any real work with it, I'm afraid). There are other materials with higher 'coolness' factors, like Nitinol or fancy designer hydrogels, but clay is one of the most interesting naturally occurring material out there. There's a few other really cool ones - blood, for example, has truly amazing fluid mechanics - but clay is still a very unique material.

illusions, can you sprinkle some of the stuff into a glass of water and report back?

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Originally Posted by Aimless

illusions, can you sprinkle some of the stuff into a glass of water and report back?

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Already did this with a bowl of water. Sculpey sand floats on the top, not like an iceberg or a boat, but like something that is hydrophobic. Additional fun can be had with smaller water droplets sprinkled on this layer of material. They form in the spheres I mentioned above and will roll around on the surface until they come into contact with a patch of uncoated water, at which point the sphere dissolves.

Edit: I almost accidentally edited your post instead of quoting it. I was wondering why there were no quotes around what you said and then noticed the poster's name was Aimless and not Illusions :bulb:

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Originally Posted by Illusions

Already did this with a bowl of water. Sculpey sand floats on the top, not like an iceberg or a boat, but like something that is hydrophobic. Additional fun can be had with smaller water droplets sprinkled on this layer of material. They form in the spheres I mentioned above and will roll around on the surface until they come into contact with a patch of uncoated water, at which point the sphere dissolves.

Edit: I almost accidentally edited your post instead of quoting it. I was wondering why there were no quotes around what you said and then noticed the poster's name was Aimless and not Illusions :bulb:

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Bad admin! Bad!

Gah, materials science. Not my forte! "Just messing with surface tension" is my contribution. :D

But I can say that I'm familiar with sculpey. Weird-ass stuff. It's also mind-boglingly light weight. Freakishly so.

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Originally Posted by wiggin

Honestly, I think clay is one of the most fascinating materials I've ever studied in my coursework (never done any real work with it, I'm afraid). There are other materials with higher 'coolness' factors, like Nitinol or fancy designer hydrogels, but clay is one of the most interesting naturally occurring material out there. There's a few other really cool ones - blood, for example, has truly amazing fluid mechanics - but clay is still a very unique material.

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Had to hold an actual lecture once during a course about self-organizing materials. There's a whole lot of interesting stuff out there. Like, why does drying mud form hexagonal plates? How do sand waves or cotton-wool clouds form?

(My own lecture was about excitation of squid neurons - so far removed from my field of study that I don't remember too much of it ;) )

And the real fun starts with magnetic fluids.