Superglue

Superglue is a substance which permanently binds objects together.  It was discovered by accident by Dr Harry Coover during the Second World War when he was working for Kodak Research Laboratories to develop optically clear plastic for gun sights.  He realised that he had made an important discovery when the substance he had produced stuck things together.

Superglue is cyanoacrylate, an acrylic resin which forms its strongest bond almost instantly.  The trigger for it to set is the presence of hydroxyl ions, OH-, from water, which is present in small amounts on the surface of nearly all solids.

 

Cyanoacrylate is a thermosetting adhesive, meaning that it cannot be heated and softened repeatedly.  As it sets it becomes permanently crosslinked, forming a tough and permanent polymer plastic.

To be an effective glue, the liquid must thoroughly wet the surface of the solid, so that there are no gaps or bubbles.  As the glue sets it creates a solid interface between the surfaces which becomes a permanent bond.

The need for water as a trigger to set explains why a thin layer of glue binds two surfaces so well - a thin layer easily obtains the water it needs from the atmosphere or the surface, while a thick layer is unable to do so.  This is also why glue sticks skin so well - it is warm and moist, providing the ideal conditions for the glue to set.

Why doesn't glue set in the tube?

In order to set, the monomer requires moisture to polymerise.  The tube contains oxygen, in the form of air, but excludes water.  Oxygen inhibits the process of polymerisation, while water catalyses it.  The presence of oxygen inside the tube therefore prevents the glue from setting.

Uses of Superglue

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Cyanoacrylate is used in criminal investigations to detect fingerprints.  The object to be tested is placed in a airtight container which is heated.  Cyanoacrylate is introduced to the container, then evaporates and is circulated by fans.  The gaseous glue reacts with materials left in fingerprints, such as amino acids and glucose, making them visible.
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Superglue is used instead of stitches to close wounds.  By changing the type of alcohol in the superglue from ethyl or methyl alcohol to butyl or octyl alcohol the compound becomes less toxic to tissue.  This is a useful application in cosmetic surgery where the appearance of scars is an important consideration.
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A similar application is found in veterinary care: tortoises have had their shells stuck back together, horses have had split hooves repaired, pigeons have had feathers glued and fish have had fins reattached.

Sticky Moments

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A Peruvian man who was wheelchair bound starved to death after accidentally gluing his teeth together.
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A prisoner suspected of breaking his bail curfew glued himself to his girlfriend in an attempt to evade arrest.
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Perhaps the stupidest superglue incident involved the couple who arrived in casualty asking to have the woman's hands removed from her partner's private parts!

Note  Should you accidentally superglue your hand to something, acetone nail polish remover usually helps to un-stick glued skin.