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Kitchen experiments with Aerogel: Moisture (7/5/08)
Introduction & Basics | Strength and composition | Optics | Moisture | Temperature | Electrical | Applications | Where to buy

  1. Aerogel, according to Wikipedia, has a "hygroscopic nature" - it attracts liquids towards it. Holding it in my fingers pulled the oil out of a spot of my skin, and left a mark on the aerogel:
    Mark left on finger by aerogel removing skin oils Mark left on aerogel by removing skin oils

    Don't worry - it goes away with a little moisturizer.

  2. The question was, how good was it at this? Tests in a closed container with a small amount of water failed to change the water level:
    Aerogel closed container test

    Another test failed to change the humidity of the air in the container:
    Aerogel humidity test

    This is aerogel on a sponge filled with water and green food die. It didn't absorb the water, so I pushed on it with my finger and this is the before and after shots, and a closeup of the result:
    Before pressing on the aerogel After pressing on the aerogel Close-up of dyed aerogel

    Notice how white it looks when removed from the sponge. The bottom has a bit of green to it but the aerogel actually filtered the dye out of the water before absorbing it further, probably due to the size of the pores. Since they absorb water the majority of them must be greater than 275 picometers1, and air which is 969pm2, but less than that of the food dye (that wasn't absorbed) which was composed of Tartrazine and Brilliant Blue FCF. Thanks to the brilliant folks at AskMeFi we know Tartrazine has a max width of 1711.0pm, and Brilliant Blue FCF is 1954pm. That puts the upper width limit of the pores somewhere between 969pm and 1711pm, a resolution of 742pm, or less than a nanometer. I think. :-)

    So it appears Aerogel, or at least the batch I had, wasn't "hygroscopic" at all. The only way I could get it to interact with a liquid, short of immersing it (see next) was to push on it, which is also what I was doing while holding it. That makes it hydrophilic (it'll bond with water) but not hygroscopic (it doesn't "attract" water from a distance). Once it's got the water it'll pull it up into it via it's pores though, sort of like the wicking nature of polypropylene socks hickers use to keep their feet dry while hiking. Lawrence Berkeley National Laboratory has a great page on the chemistry for those who are curious.

  3. Dropping it in a liquid is a recipe for disaster. It overpowers it and clouds the contact area while pushing air out, which makes a noise like rice krispies do when milk is added. I tried water, acetic acid (vinegar) and oil, and all looked like this:
    Aerogel dropped in water

    The oil enabled me to figure this out since it acted slow enough I could better see what was happening. While it looks as though the aerogel has "collapsed" instead the collapsed section is actually regular aerogel (it's see-through, remember?), and the wet areas are, well, wet. Air forced out of the air pockets created the bubbles all around it. The oil one was actually completely silent and I could watch the air bubbles slowly try to escape their air pockets:
    Air bubbles trying to escape aerogel pores after being dropped in oil

    Under more (good catch malloc!) less viscous fluids like water and vinegar the air purged in seconds (making the Rice Krispies noise).

    Here's the result, in water (vinegar looked the same) and then oil:
    Result of aerogel being dropped in water Result of aerogel being dropped in oil

    Aerogel that has been "collapsed" by a liquid crumbles easily. It'll still be wet, and far smaller than it was before getting wet, but can be dried out. After drying the cloudiness didn't go away. See below for information on temperature experiments on these.

  4. I tried a few lower surface tension fluids like ethyl alcohol but still had the same problem. I stopped short of going to more obscure chemicals generally unavailable to the home experimenter. LBL has a page about aerogel surface chemistry and towards the end it says:

    "Fortunately, this problem can be easily circumvented by converting the surface hydroxyl (-OH) groups to a non-polar (-OR) group. This is effective when R is one of many possible aliphatic groups, although trimethylsilyl- groups are the most common. The derivitization can be performed before (on the wet gel) or after (on the aerogel) supercritical drying. This completely protects the aerogel from damage by liquid water by eliminating the attractive forces between water and the silica surface."

    So it sounds as though something can be done to protect the aerogel against liquids. I just don't have a clue what their talking about... no chemistry degree! I was led to "Silanizing glassware" as a possible means of accomplishing this, and an easy version was said to be Rain-X (far left):
    Aerogel after Rain-X

    Oddly, the clear one in the middle is from water while that blue smudge on the right is regular aerogel. So I'm starting to wonder if the size of the aerogel is part of the mystery here. Regardless, after drying, the Rain-X one was as white as table salt!
    Dried aerogel after Rain-X

    Then I saw "How to make magic sand" on Youtube. Sand is silicone, so is glass, aerogel is glass... why not? They used Scotch Guard for it.
    Aerogel being sprayed with Scotch Guard

    Which gave it a really cool texture, but nearly the same result as Rain-X:
    Aerogel after being sprayed with Scotch Guard

    The last idea I had, but ran out of Aerogel, is just your regular lacquer or whatever. I worry that'll disrupt its other abilities though.

Introduction & Basics | Strength and composition | Optics | Moisture | Temperature | Electrical | Applications | Where to buy

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- Kitchen experiments with Aerogel: Introduction & Basics (7/5/08)
   * Kitchen experiments with Aerogel: Strength and composition (7/5/08)
   * Kitchen experiments with Aerogel: Optics (7/5/08)
   * Kitchen experiments with Aerogel: Moisture (7/5/08)
   * Kitchen experiments with Aerogel: Temperature (7/5/08)
   * Kitchen experiments with Aerogel: Electrical (7/5/08)
   * Kitchen experiments with Aerogel: Applications (8/25/08)
   * Kitchen experiments with Aerogel: Where to buy (8/25/08)
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