Glue Are You?

Apr 01 2011 Published by under Uncategorized

On my first post below, Bob O’Hara commented that I must be sad at the passing of the inventor of superglue.  Yes, I’m sad but what a legacy to leave behind.  Like many discoveries, superglue was discovered by chance whilst looking for something else.  Two scientists working for the Kodak laboratories in 1942 were trying to find a transparent plastic (which is a polymer with additives in it) that could be used for gun sights.  Dr Harry Coover, who sadly died last week, and Fred Joyner discovered that compounds called cyanoacrylates could stick pretty much anything together.  Cyanoacrylate refers to the key parts of the molecules and a few different variations can be made.  When cyanoacrylates come into contact with small molecules like water, they polymerise up to form long chains.  That’s why superglue has to be kept in a moisture free container.   Polymerisation is the process where lots of small molecules, called monomers, react with one another to form long polymers.  These long chains bond the surfaces together when used as a glue.

Methyl cyanoacrylate.  The 'methyl' bit is the CH3 on the right.  The 'cyano' bit is the N with three lines drawn to the next atom which is a carbon (by convention, not shown, just represented by a bend in the line or a change from multiple bonds to single bonds).  Cyano sounds a bit like cyanide and they have the same elements but are very different in behaviour.  Cyanide is a N, nitrogen atom, with three lines (bonds) to C, carbon and a negative charge.  In this molecule the CN bit is very tightly bonded to the rest of the molecule and therefore very different to cyanide.The acrylate bit is basically the rest of the molecule!




This is what happens when molecules like the one above join up to form a polymer.  The R groups at the bottom can be methyl like above, or another organic group.  These polymers can be very long molecules with molecular masses many hundreds of thousands of times heavier than water.

A lot of people use superglue to seal cuts, and some people may recall an episode of House set at the South Pole where the base medic seals a wound in a workers leg with superglue.  Medical grade superglue is available, and the main difference is a long chain added onto the monomers.  This makes the glue less irritating to the skin when applied.



2- Octyl acryalte.  This is the monomer that may be used in medical grade products.  The main difference is the methyl group has been replaced by a much longer octyl group that behaves like an oil.



Superglue is also quite commonly used in forensic science applications where it is used to enhance latent fingerprints on non-porous surfaces like glass or metal.  In this case the monomers are warmed gently (many having boiling points below that of water), and the fumes rise up and react with substances left behind in the fingerprint, and with moisture from the air.  This leaves a thin film of white polymer where contact with the fingerprint substances was made, allowing the ridge detail to be visualised and the print compared to reference prints.

The great thing about people like Dr Harry Coover, and the hundreds of researchers and scientists like him, is that they leave behind things that make small yet measurable differences in people’s lives.  Your world might not end because you can’t stick something back together, but its probably better when you can, because of products like Superglue.



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