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Material inflation

  1. Dec 16, 2015 #1
    I have observed that certain materials can drive fluids into themselves and push their own molecules apart, thus inflating itself. When, I try to reason, I'm not quite successful. Even if there is surface tension or under atm pressure, extension of intermol. distance is departure from equilibrium, which I'm not sure is supposed to happen. If it is already internally stressed, then it must also eat up surrounding air, but it does that only with water.
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  3. Dec 16, 2015 #2


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    Which materials?

    A dry compressed bath sponge will expand when wet. Is that what you are taking about?
  4. Dec 16, 2015 #3
    Are you talking about swelling of elastomers?
  5. Dec 16, 2015 #4
    Doctors in the czech republic have demonstrated desirable results for weight loss using what reporters are calling "balloon pill". It is a pill that takes up portion of stomach volume thus enforcing reduced ingestion. Maybe it is termed swelling elastomer. I don't know, but what maybe the mechanism of action? Purely static pressure reducing density by driving out air until elastomer tension equals water force?
  6. Dec 16, 2015 #5
    Google "swelling of elastomers" and "swelling of rubber" for a description of the mechanism.
  7. Dec 16, 2015 #6
    Here's a rough description of the mechanism. The polymer and the solvent tend to be mutually soluble, and, under ordinary circumstances, their molecules would totally intermingle. However, in the case of an elastomer, the polymer is cross linked, and there are polymer chains between cross links. These polymer chains act as little springs. So, when the solvent tries to intermingle with the polymer, it is able to do so only to a limited extent, because the structure is held together by the springs. The amount of solvent that the elastomer can take up is limited by how much the chains stretch. There is a balance between the driving force for the solvent molecules to enter and intermingle with the polymer, and the action of the chains (between cross links) to try to squeeze the solvent out of the structure. The net result is an equilibrium featuring a swollen cross linked polymer containing solvent molecules within its structure.
  8. Dec 17, 2015 #7


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    Some 30 years ago some vandals broke into an Army Cadet building and ate the contents of a survival pack. I was told the pack contained some sort of compressed oat biscuit that was designed to swell up and make 6 pints of porridge when mixed with water. So perhaps it was fortunate that they also ate the laxative chocolate.
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