132 Adhesives

How Do Adhesives Work?

Adhesives are the unsung heroes of infrastructure and human society. The developments in infrastructure and technology that have come about from bonding two surfaces together are innumerous, from construction, to transport and even space travel. In this article, we discuss the development and application of modern adhesives.

The process of refining natural adhesives went relatively unchanged for thousands of years. Animal parts were boiled down into a gelatinous form, which was dried into powder and mixed with water to achieve the desired consistency. World War Two saw a breakthrough in understanding of plastics and rubbers and led to the accidental creation of cyanoacrylate glue, also known as superglue. Cyanoacrylate glue was the first of the many types of polymer-based glues that are available today.

Adhesives rely on two forces to work – cohesive and adhesive force. Adhesive force is the strength at which the glue sticks to a surface, and cohesive force is how well it stays together. There are several ways in which glue bonds two surfaces together.

Adsorption

This is considered the weakest form of adhesion, however it is practical in other applications. Adsorption works by spreading the glue as a liquid so it completely covers a surface. When another surface comes into contact, millions of microscopic electromagnetic links are made between them, holding the two surfaces together. However, adsorption is good for trapping microscopic particles; objects that use adsorption in this way include silica packets, gas masks and water filters.

Chemisorption

This method of adhesion is much stronger and more common than adsorption. With chemisorption, the surface of an object is broken down at a molecular level and combines with the other surface; most polymer based glues work this way. There are several ways to prevent chemisorption from happening too early and destroying the container the glue is stored in. The most common ways are with the use of solvents, or by keeping the adhesive’s active ingredients separate while stored.

Mechanical

Mechanical adhesion can only happen on porous surfaces. When the glue is applied, it fills the holes of the surface before drying, gripping it together. Mechanical glues rely on strong cohesive forces to hold surface together.

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