Superglue is an incredibly useful invention, allowing us to repair all manner of objects. However, it nearly wasn’t invented at all! Here’s a quick look at the story of superglue, and, more importantly, the chemistry that allows it to do its job.
Superglue was initially discovered by accident. Dr Harry Coover, a researcher at Kodak laboratories, was trying to develop clearer plastics for use as gunsights during the Second World War when he stumbled across cyanoacrylates, the class of chemicals used in superglue. However, due to their tendency to stick to absolutely anything, they were discarded as useless.
The story of superglue might have ended there, but Coover was also involved in the rediscovery of cyanoacrylates several years later. This time, it was during research in the early 1950s into flame-resistant polymers for use in jet canopies. A research student working under Coover synthesised ethyl cyanoacrylate, and, in trying to measure the compound’s refractive index, accidentally stuck two glass prisms together. This time around, Coover realised the potential of the cyanoacrylates, and they were eventually developed into a super-adhesive glue that was made available commercially in 1958.
So, how do the cyanoacrylates lend superglue its stickiness? Simply put, these compounds can react with small amounts of water – even the amount of water present as water vapour in the air is enough to initiate a reaction. The reaction between a cyanoacrylate and water produces an intermediate ion which can go on to react with more cyanoacrylate molecules, eventually created a long chain of them all connected together – a polymer. This is different from many other glues, which form a bond as the solvent they are carried in evaporates.
The reaction with water is also the reason that getting superglue onto your skin can easily end badly. As your skin contains moisture, it too can set off the polymerisation reaction. There’s a very good reason why superglue packets warn you not to get it anywhere near your eyes or mouth!
The polymer superglue forms is very strong, making the glue very difficult to tear apart once it has set. Intermolecular forces (such as Van der Waals forces) between the glue and the surfaces you’re attempting to stick together help hold it in place. Mechanical binding also plays a part: the glue can seep into small cracks and pores on the surfaces being stuck together, and when it solidifies this too becomes very difficult to pull apart. In truth, we still don’t know all of the details when it comes to understanding how glues stick surfaces together; though we have a general idea of the forces involved, the nature of these forces for particular glues still isn’t fully understood.
The cyanoacrylates actually have more uses that just in superglue. Some of them can also be used to help stick wounds together, particularly in combat situations where temporary fixes for lacerations until stitches can be put in are often necessary. Different members of the compound class which are less irritating to the skin are used for this, such as 2-octyl cyanoacrylate. Cyanoacrylates can also be used in dentistry, to create some types of fillings.
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References & Further Reading
- Organic chemistry – W Brown & others
- Molecule of the month: cyanoacrylate – S Baig
- Glue are you? – K J Haxton, Scientopia