How blue-tack sticks?

  1. suppose we have a very smooth and hard surface such as mirror, and we stick a blue tack on it.

    there is no chemical reaction. what force keeps it stuck?

    is it electromagnetic?
     
  2. jcsd
  3. brewnog

    brewnog 2,791
    Science Advisor
    Gold Member

    It's not electromagnetic as such, although there are certainly electromagnetic forces which play a part in the bonding within the substance.

    It's just sticky! Long-chain hydrocarbon polymers often form these gooey, sticky substances. Turning them into a usable product is just a case of getting the right balance of tackiness, without being too sticky.


    http://www.madsci.org/posts/archives/Jan2003/1043271591.Ph.r.html
     
  4. DaveC426913

    DaveC426913 16,310
    Gold Member

    A good reference Brewnog, but for my money "becasue it's sticky" isn't really an answer. What does it mean for something to be sticky?

    I found the answer (or at least, the author's belief) in your link:

    "...Hydrocarbon polymers is the adhesive component in Blu-Tack. Polymers tend
    to be pretty sticky; they are long chained hydrocarbons that have lots of
    hydrogen on the surface that tend to form physical bonds with anything
    that they come in contact with
    ..."
     
  5. Hi there,
    I'm also very interested in the mechanism of blu-tack.
    I don't really understand why hydrocarbon polymers are adhesive. From my chemistry knowledge, hydrocarbon polymers are supposed to be non-polar, leave alone forming hydrogen bonds. Their nature should be like oil - slippery instead of sticky.
    However, let's assume it is a long carbon chain with a lot of OH groups attached. How do you explain then, that blu-tack also sticks to smooth non-polar substances? No hydrogen bonds are supposed to be formed. I am still very confused.
    Moreover, blu-tack has the property of being elastic, yet capable of being molded. Is its molecular structure like that of metal, which recoils by electrostatic force, or is it like a rubber band, which recoils due to thermo-energy?

    source: http://en.wikipedia.org/wiki/Natural_rubber#Properties
    In most elastic materials, such as metals used in springs, the elastic behavior is caused by bond distortions. When force is applied, bond lengths deviate from the (minimum energy) equilibrium and strain energy is stored electrostatically. Rubber is often assumed to behave in the same way, but it turns out this is a poor description. Rubber is a curious material because, unlike metals, strain energy is stored thermally.
     
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