Harry Wesley Coover Jr., the inventor of “Super Glue” recently passed away at the age of 94. Super Glue is an adhesive with extraordinary bonding capabilities – just a couple of drops of the liquid and you can virtually glue anything together permanently! Remember the construction worker holding onto his helmet which is attached only by a drop of glue to a beam? A bit of creative marketing here unless the worker had super strength in his arms. But the glue really could hold that kind of weight. It can even be used to glue skin together instead of sutures!
As with many inventions, superglue was an accidental discovery. During WWII, Dr. Coover and colleagues were trying to find a way to use clear plastic to make gun sights for weapons out of a particular kind of plastic known as polycyanoacrylate. However, Coover found cyanoacrylates too sticky to work with and discounted them. Later, in 1941, while working for the Eastman Kodak Company, Coover found that the stickiness of cyanoacrylates came in handy in the manufacture of plastic canopies for jet planes. Coover and Kodak subsequently refined the substance and commercialized it as a glue. The chemistry here is fascinating. The tube of Super Glue doesn’t actually contain glue. It contains a chemical, usually ethylcyanoacrylate, that forms the glue once it comes into contact with moisture in the air. It is water that initiates a reaction by which the small ethylcyanoacrylate molecules join together to form polyethylcyanoacrylate which is the actual glue. This is also the reason why it can be frustrating to keep a tube of cyanoacrylate glue from hardening. Once it is opened, moisture inevitably enters and converts the monomers to a hard polymer. High humidity causes the glue to set quickly, explaining why it is harder to keep an open tube from clogging up in Miami than in Denver.
In 1977 another amazing property of cyanoacrylate glue was discovered. It could reveal latent fingerprints! Trace evidence examiner Fuseo Matsumara from the National Police Agency of Japan noticed his own fingerprints developing on microscope slides while he used cyanoacrylate glue to mount hairs from a taxi driver murder case. Matsumara later relayed this information to his colleague Masato Soba, who developed the cyanoacrylate fuming method.
So how are latent fingerprints recovered with superglue fumes? Fingerprints are composed of several chemicals exuded through the pores in the fingertips and are left on virtually every object touched. The primary component of latent fingerprints is sweat, which is mostly water, and will dry out after a short period of time. The other components are mainly solid and will remain on the surface for a much longer period of time. These solids include organic compounds like amino acids, glucose, lactic acid, peptides, and inorganic chemicals such as potassium and sodium salts. The item featuring the invisible fingerprints is placed inside a compartment where super glue is heated to the point of vaporization (54-56 C). Once the superglue vapor interacts with the chemicals left behind by the suspect, a visible, hard, white substance is formed on the ridges of the print. At this point, the crime lab technician can photograph and analyze the print. Unfortunately, the superglue fuming method isn’t that simple and does come with caveats. The process can take up to five hours, so investigators commonly use accelerating methods to alter the heating process or the atmospheric pressure inside the container. And once the fingerprints have been visualized, the fumes must be vented out of the container by high-powered fans because superglue fumes are highly irritating and flammable. Furthermore, its combustion can produce lethal amounts of cyanide gas. Nevertheless, superglue has helped put many criminals away, while exonerating some innocents. Just a year ago, in 1910 President Obama honoured Dr. Coover with the National Medal of Science.