What Makes Superglue so Super?
There is always a commercial that I watched when I was a kid that pops back into my memory. In the commercial, some people apply a line of material ontoa plank. In the next second a motorcycle rushes to the plank and then raises the front wheel toward the plank. And guess what happened? Amazingly, the motorcycle firmly attached to the plank in a second. How did this happen? What did the people put onto the plank? The people had applied a material called superglue. Superglue definitely deserves its name; a one-quarter-inch bond can hold more than a ton. But, what makes superglue so super?
The main ingredient in superglue is cyanoacrylate. It is an acrylic resin that cures almost instantly just like in the commercial. Cyanoacrylate is a polymer that consists of monomersof cyanoacrylate molecules. There are two main types of monomers, one is methyl-2-cyanoacrylate (CH2=C(CN)COOCH3or C5H5NO2) and the other one is ethyl 2-cyanoacrylate (C6H7NO2). They contain several identical functional groups: an ester, a nitrile and an alkene. The only structural differenceis in the substituents of the alkyl group connected to the single bonded oxygen of the ester.One is a methyl group and the other is an ethyl group. This structural difference causes a difference in the molecular weight and density. Methyl-2-cyanoacrylate has a molecular weight of 111.1g/mol and a density of 1.1 g/mL, which is slightly higher than water. The flash point, which is the lowest temperature at which it can vaporize to forman ignitable mixture in air, is 79 °C.Ethyl 2-cyanoacrylatehas a molecular weight of 125g/mol, a density of 1.06 g/mL, and a flash point of 75 °C. Both of them have the similar chemical properties due to the similar structure. The flash points of the cyanoacrylates indicate that the best temperature to use cyanoacrylate should be under it. The fact that the flashpoints are above 70 °C means that supergluecan be widely used since it is nowhere near room temperature.
What allows superglue to work immediately? How come the motorcycle cannot move once it attached to the superglue? Cyanoacrylate can undergo a process called anionic polymerization rapidly in the presence of water. Anionic polymerization a process of reacting repeated cyanoacrylate molecules together in a chemical reaction to form long and strong chains that join the bonded surface firmly together. “Anionic” specifically indicates the hydroxide ions here, which come from water. The hydroxide ionsact as a nucleophile here, which is an electron-rich group. It attacks the electron-poor alkene group to break the double bond. The carbon now becomes negatively charged and it acts as a nucleophile just like the hydroxide group.The carbon attacksthe alkene group of a new cyanoacrylate molecule. This attack by the hydroxide ion and carbon continues until a large polymer of cyanoacrylate is formed. The only thing needed to trigger the polymerization is the hydroxide group. It’s convenient to obtain the hydroxide group since comes from water. The object you might wish to glue has at least some trace amounts of water on its surface.Hydroxide ions can also be trapped from air in the form of humidity. Because the cyanoacrylate is applied thinly, it can ensure that the reaction proceeds rapidly and a strong bond is formed within a reasonable amount of time.
However superglue is not always super. A disadvantage of superglue is that it has a short shelf life. Superglue has a shelf life of about one year from the manufactured date if unopened, and one month once it is opened. Because the presence of moisture causes the glue to set, exposure to normal levels of humidity in the air causes a thin skin to start to form within seconds. The inner superglue also generally undergoes the reaction although it is much slower than the surface one. Finally superglue needs to be discarded after only one use because its nozzle gets clogged and the content becomes partially solid. The reaction with moisture can cause a container of superglue which has been opened and resealed to become unusable more quickly than if it was never opened. You can also find that even if you tighten the lid after use, you may not be able to open it again because the opening of the glue tube and the lid stick to each other so tightly. So we have to look for a better way to prevent this from happening. Here are some tips to minimize this reductionin shelf life of cyanoacrylate: Once opened, you can storeyour superglue in an airtight container with a package ofsilica gel desiccant, which you can easily obtain from some food packages. The silica gel desiccantreduces the chances of the cyanoacrylate to be in contact with water. Another way is to insert a hypodermic needle into the opening of a tube instead of using the cap of superglue. After using the glue, residual glue soon clogs the needle, keeping moisture out. The clog is removed by heating the needle before use. The fact that the shelf life of superglue is less than desirable might be the reason of why superglue typically comes in small packages.
Under normal circumstances, cyanoacrylate is a liquid. To facilitate easy handling and make it looklike glue, a cyanoacrylate adhesive is frequently formulated with an ingredient such asfumed silicato make it moreviscousor gel-like. Fumed silica is a powder that is produced in a flame. It has an extremely low bulk density and high surface area that help in increasing viscosity. More recently, formulations are available with additives to increase shear strength, creating a more impact resistant bond. The manufacturer adds rubber or other additives to superglues to increase viscosity and make it more gel-like.
What makes superglue different from the other normal glues? White glues, such as Aleene’s, whichis typically used for handcrafting makesbonds bysolvent evaporation. The solvent in Aleene'squick dry tacky glue is water. So you can see the paper soaked wavy when you apply white glue to it. As the water evaporates, the polyvinyl acetate latex, which is the ingredient of white glue, spreads into a material's crevices to form a flexible bond.Since the water cannot evaporate fast, it takes time to wait for it to dry. So it is not as fast as superglue to be dried. After it dries, you can peel entire glue out of the surface if you apply it to some smooth surface, such as plastic. Super glue, on the other hand, undergoes a process of anionic polymerizationas was mentioned above. Cyanoacrylate molecules start linking up when they come into contact with water, and they whip around in chains to form a durable plastic mesh. The glue thickens and hardens until the thrashing molecular strands can no longer move.
While superglue will fix the broken coffee cup forever, it could also stick to your fingers very easily. There are however some tips to get rid of superglue from your skin.Cyanoacrylate is impervious to water, but it can be dissolved with an organic solvent, such as acetone. Using this property, we can imagine how easy it is to remove the annoying superglue from your finger. Some nail polish removers contain acetone.But be sure to check the label, since many acetone free products are available and these will not work against superglue. It’s also possible to find pure acetone in stores that sell home supplies or art supplies, because acetone is such a useful solvent that you can use it to remove marks from a permanent marker. However, acetone is flammable and toxic, so it’s not a chemical you want to ingest or inhale. It is absorbed into skin on contact. It dehydrates and defats skin, so wash any spill with soap and water and apply a moisturizer, if possible.
There are often incomprehensible plots in some movies that involve superglue. For example, in the movie Young and Dangerous,someone’s mouth is sealed with superglue. I wonder if I was the victim how would I go about getting rid of the superglue and be able to talk again. In real life, it barely happens. However, if you need to get rid of superglue on your lips, you cannot use acetone since it is toxic. But you can apply a generous amount of warm water and encourage maximum wetting and pressure from saliva from inside the mouth. You can try to peel or roll your lips apart. Don’t worry about swallowing the minor toxic superglue by accident, because it is almost impossible to swallow the adhesive as a liquid. The superglue adhesive solidifies upon contact with saliva due to moisture and it can adhere to the inside of the mouth. Saliva will lift the adhesive in one to two days. However, try to avoid swallowing the adhesive after detachment.
Meanwhile, you can also feel a heat from your fingertips when superglue drops on it. Because the chemical process of polymerizationproduces a certain amount of heat during the reaction, you should be cautious of not applying too much superglue at once. If a large enough amount of super glue makes contact with your skin, it can potentially cause burns.
Superglue is not only used for adhesives, its properties are applied to many areas. Since cyanoacrylate has a low shearing strength, it has led to its use as a temporary adhesive in cases where the piece needs to be sheared off later. And also you may notice after a few times of using superglue thatthinner layer bonds more effectively than a thicker one. For a thicker layer, you have to wait for longer periods of time to allow the inner side of the thicker amount of superglue to be dried.This definitely makes superglue lose one of its main advantages of being instant.
One of the fancy applications of superglue other than just pasting is superglue fuming, which is a superglue method to collect fingerprints that I watched in agangster film. In the criminal investigation, the police use smoke of cyanoacrylate to identify potential fingerprints. An item that may have fingerprints is placed in a heated and airtight container. Then, superglue is placed into the container and the cyanoacrylate evaporates. The laboratory personnel will use the fan to circulate the cyanoacrylate in the container. As the cyanoacrylate circulates the residue materials in fingerprints such as amino acids and glucose will react with the gasification of cyanoacrylate and make a fingerprint rendering. Isn’t it useful? Again, superglue deserves its name.
Note: Try adding a paragraph on the history of superglue. Who invented superglue? When?
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