This article explains how adhesives, which are widely used in everyday life, bind materials together, and discusses their scientific principles, types, and possible applications in various industrial and medical fields.
We use many tools in our daily lives. We use scissors to cut something, we use a pen to write, and when our new hairpin falls off, we use a bond to reattach it. Scissors and writing instruments have been around for a long time, and their role and workings are relatively simple. Bonds and adhesives, on the other hand, are relatively new technologies that provide important conveniences in our lives. When we use bonds or adhesives to attach something, we’re not just joining two objects together, we’re also considering how strong the bond is and how long it can last. There are many scientific principles behind the act of cutting, writing, and gluing something. In this article, we’ll explain how one of the most common tools we use in our daily lives works: glue.
We’ve all wondered at one point or another how glue works to hold two substances together. Before we dive into how glue works, let’s talk about the definition of adhesion. Adhesion is a state in which two substances are united by chemical or physical forces or both. In other words, the intermolecular attraction of the polymers in the adhesive creates the bond. To understand this process, we first need a basic understanding of the structure and interactions of molecules. A polymer is literally a molecule with a high molecular weight, i.e., a long molecular length. Intermolecular attraction refers to the interactions between neighboring molecules, rather than the forces that hold atoms together (chemical bonds). These interactions are electromagnetic in nature, and the larger the size of the molecules and the shorter the distance between them, the stronger they are. This is why polymers with large molecular sizes are the mainstay of adhesives.
Typical adhesives are dissolved in a solvent, most often water. The water acts as a carrier for the polymer, carrying the polymer and seeping into the tissue of the adhesive material. Once the water is gone, the polymers in the adhesive use their mutual attraction to hold the two materials together. However, if too much adhesive is used, the polymers in the adhesive will push against each other, preventing the polymers from working together properly. In addition, too much adhesive makes it difficult for the solvent, water, to volatilize. The thicker the adhesive is applied, the less effective it is. This is because the principle of adhesives is intermolecular interaction, not their own viscosity.
To understand the different ways in which adhesives can be used, it’s important to have a deeper understanding of their mechanism of action. For example, the performance of adhesives can be greatly affected by environmental factors such as temperature and humidity. When using adhesives, the surrounding environmental conditions must be carefully considered, and certain situations may require specialized adhesives. Different types of adhesives are suitable for different conditions, and different adhesives have been developed to meet these conditions.
The same principle explains why adhesives in containers may or may not adhere to themselves or to the walls of the container. The polymers in the container are dissolved in a solvent, such as water. At this point, the polymers are far apart from each other. As explained above, intermolecular attraction is stronger the shorter the distance between molecules, so if water is trapped between the polymers, the attraction will be smaller. Also, adhesives are not typically direct polymers. When a small molecule dissolved in a solvent meets oxygen from the air, it spontaneously converts into a polymer through a condensation reaction to form an adhesive. When storing adhesives, it is necessary to add a substance that inhibits the condensation reaction to prevent self-sticking. In the case of old adhesives, these condensation inhibitors volatilize, causing the adhesive to harden and deteriorate.
Adhesives can be categorized into three main types. First, there are adhesives that use polymers such as starch or rubber as a solution; then there are adhesives that are initially a liquid of small molecules that polymerize into a polymer after use; and finally, there are adhesives that melt solids of polymers by heating them. This diversity stems from the unique chemical properties of each adhesive. These properties are tailored to different applications, some of which have become indispensable in certain industries.
Epoxy resins, which are widely used in everyday life and industrial production, are the second type. Epoxy resins are a class of synthetic resins, and they come in a wide variety of products, ranging from liquid to solid, depending on their melting point. The most common commercially used epoxy resins are the ether type, which is produced by a condensation reaction with DPP, popularly known as ECH and BPA. In simple terms, ECH and BPA are small molecules that meet and react in the presence of sodium hydroxide to produce a polymer that can act as an adhesive. Because these epoxy resins offer strong adhesion and durability, they are often used in highly technical fields such as automotive and aircraft parts and building materials.
Adhesives are widely used. Epoxy resins alone, for example, produce about 15 billion different types of adhesives annually. Manufacturing, semiconductor processing, and military applications also require a lot of adhesion, and there is a suitable adhesive for every situation. The continued growth of the adhesive industry is also closely linked to the development of new materials. As new materials are developed, so is the research and development of adhesives to effectively bond them together. Adhesives are not only used in traditional applications, but also in a variety of new fields.
In addition to traditional bonding applications, adhesives are also being used in ingenious new areas. Steam pipes on ships are highly corrosive due to high temperatures and prolonged immersion in salt solutions. In addition, strong vibration of screwed parts accelerates corrosion. In this case, applying a suitable adhesive between the parts and securing them with screws can make the bond stronger and prevent corrosion. In the bio area, adhesives such as patches are also increasingly used. From the patches that many people use to treat acne, adhesives have recently been invented that can be used to bond hearts. These adhesives are expected to be used in cardiac surgery, gynecology, and abdominal surgery. These bioadhesives are composed of substances that are harmless to the human body and play an important role in reducing recovery time and preventing infections at the surgical site. In modern medicine, adhesives are becoming more than just an industrial tool, but an important tool in biotechnology.
