If glue is so sticky, why doesn't it stick itself to the bottle?

Audit expert: Luo Huiqian

Researcher at the Institute of Physics, Chinese Academy of Sciences, science writer

Glue is one of the most common bonding tools in daily life. Whether it is ordinary office glue or the extremely high-performance 502 glue, they have two things in common: they are all liquid and sticky. Have you ever wondered why glue is always liquid? If glue is so sticky, why doesn't it stick to the bottle?

Source: pixabay

1

What is glue?

The essence of glue is an adhesive, that is, a medium that can make two objects stick together. Humans discovered the bonding effect in ancient times.

According to archaeological discoveries, as early as 5,300 years ago, humans learned to mix soil and clay to glue stones together. 4,000 years ago, my country used raw lacquer as an adhesive to make utensils.

3,000 years ago, the Zhou Dynasty used animal glue to glue the hull. The foundation stone of the Great Wall, which is well known to everyone, was made by mixing glutinous rice flour and lime in the Qin Dynasty. In ancient Egypt, people had learned to extract natural glue from plants and animals, such as gum arabic from acacia trees, rosin from pine trees, and bone glue from bird eggs and animal bones.

Later, with the advancement of technology, people created synthetic glue. In 1909, Baekeland created industrial phenolic resin, which was the beginning of synthetic resin glue. In the 1950s, people invented epoxy resin glue, which has many types, high strength and strong adaptability, and has become people's favorite type of glue. Until now, there are countless brands of glue on the market, so how do they work?

Source: freepic

Synthetic glue is more viscous and durable. The adhesion between objects is actually achieved by the chemical substances in the glue. There are usually some round polymer particles in the glue, with a radius of about 0.5-5 nanometers. They are the adhesives in the glue. If these adhesives exist alone, people cannot use them freely and conveniently. Therefore, in order to use glue more conveniently, people use water as a solvent to blend these polymer adhesives into it.

When people apply glue to the surface of an object, the polymer adhesive will penetrate into the surface tissue of the object along with the water. When the solvent, that is, water, disappears, the polymers can form mutual tension , which is why they can stick two objects tightly together. Some industrial glues use solvents other than water, but use more volatile organic solvents instead of water.

2

Why won't the glue stick to the bottle?

Why doesn't glue stick to the bottle? As mentioned above, glue is mainly composed of adhesives and solvents (water or other organic liquids). The presence of water will inhibit the adhesive from working. When the glue is poured out, as the water evaporates, the adhesives in the glue can interact better with each other, and the viscosity will be stronger. Of course, the material of the glue bottle is also specially selected according to the activity of the glue. They are generally inert materials that are not easy to react chemically with the glue , so they are also more stable and safe.

Glue bottle source丨freepic

Sometimes, if too much glue is used, the viscosity will be poor. This is because too much glue will not only make it difficult for the moisture between the polymers to evaporate, but also make the polymers crowded together, thus failing to form a strong pulling force, and the bonding effect will be greatly reduced.

However, the situation of 502 glue is different. The main component of 502 glue is α-cyanoacrylate ethyl. When it comes into contact with water and air, it will undergo a polymerization reaction and stick to other objects. 502 glue is packed in a relatively closed bottle. There are no conditions required for polymerization reaction , so it will not stick in the bottle. But when it is poured out, polymerization reaction occurs, thus sticking to objects. Sweat, hydroxyl groups, etc. on human hands can also trigger polymerization reaction, which is why 502 glue is particularly easy to stick to hands.

Chemical formula of cyanoacrylate from Wikipedia

3

What should I do if I'm stuck with glue?

When using glue, it is easy to get it on your hands. For general office glue, they are not very sticky. If you accidentally get it on your hands, you can wash it with water or rub it with your hands to remove it. However, 502 glue is different. I believe that friends who have experienced it will be afraid. If you get it on your hands, if you don’t use the right method, you may really lose a layer of skin.

502 glue

Source: A shopping website

If your hands get stuck accidentally when using 502 glue, you can use warm water to soften the glue, or wipe or wet the stuck area with alcohol, and then remove the glue by rubbing or kneading . Both warm water and alcohol can irritate the skin, thereby reducing the effective contact area between the skin and the glue, making it easier to remove the glue.

In addition to this method, there are also folk methods of using nail polish remover, wind oil, and vinegar. Among them, nail polish remover works best. This is because nail polish remover contains acetone, which is a commonly used organic solvent that can dissolve some glue. But if these conventional methods can't handle it, or the area of ​​skin stuck to the glue is too large, you have to go to the hospital and let the doctor handle it. Remember not to force the adhesive apart, otherwise you will be the only one who suffers in the end.