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Super Glue

Why does glue on your fingers stick together so quickly, but not to the inside of the tube? Learn more on this Moment of Science.

Finger glued to hand

Photo: jspad (flickr)

Moisture from the air, or in this case, skin, is needed for SuperGlue to function properly

If you’ve ever had a spill while working with SuperGlue®, you know that the warning on the side of the tube is the absolute truth: SuperGlue will indeed bond skin in a matter of seconds.

You may have wondered, as you were trying to pry your fingers apart, exactly why SuperGlue is so good at bonding skin together. Why does it glue your fingers together so quickly, but not stick to the inside of the tube?

SuperGlue is the brand name of a type of glue made from a chemical called cyano-acrylate monomer. Cyano-acrylate monomers have some properties that are especially interesting to glue manufacturers.

Monomers are small molecules that can join together to form long chemical chains. These chains, known as polymers, are pretty common in everyday life. For example, all plastics are made from polymer chains of simple molecules, as are all synthetic fabrics.

What makes the cyano-acrylate monomer so special, is the speed with which it forms polymers, and the fact that as it joins together, it tends to lock everything else around it into place as well. This rapid transformation from liquid monomer, to solid polymer requires the presence of water to get things started, be it in the air or on your skin. Without a little moisture, SuperGlue can’t bond anything.

This explains why the glue is so good at sticking fingers together. Our skin is naturally moist, and this moisture is just what those monomers are waiting for. As long as no moisture gets into the tube, however, it will stay an unsticky liquid for a long time.

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