How Adhesives Work
What is the Difference Between Adhesion and Pressure-Sensitive Adhesion?

Adhesives and pressure-sensitive adhesives are an indispensable part of our everyday lives, but they have different uses and applications. This article will explain how objects stick together and the difference between adhesion and pressure-sensitive adhesion.

How Adhesion Works

When two objects stick together, three adhesion phenomena occur on the surface.

Anchor Effect

Materials have an uneven surface that is not visible to the naked eye. The adhesive finds its way into these tiny pores on the substrate's surface and solidifies. Once the adhesive fills in the gaps, this creates an effect similar to that of a ship's anchor digging into the seafloor, allowing the two objects to hold together. The ease with which an adhesive can spread over a given substrate and maintain contact is called “wetting.” The better the adhesive material blends with the adherend, the higher the wettability.

Intermolecular Forces (Van der Waals Forces)

When an adhesive and adherend come into proximity, the force of attraction between molecules can cause the surfaces to stick together. Because the attractive forces between molecules (intermolecular forces) are extremely weak, they only work when objects are close to each other. Adhesives are designed to make better contact with uneven surfaces, creating more points of contact with the adherend, which allows the intermolecular forces to take effect.

Chemical Reactions

Chemical reactions may occur between the adhesive and the adherend surface. These reactions bond molecules to each other and allows things to stick together. Chemical adhesion is said to be the strongest mechanism of adhesion.

What is the Difference Between Adhesion and Pressure-Sensitive Adhesion?

Adhesion and pressure-sensitive adhesion are both methods for sticking objects together, but they have different properties.

What is Adhesion?

Picture a scenario where you might use glue or an instant adhesive. The adhesive is initially applied in liquid form to the object to be attached, and then the objects are stuck together. After the objects are joined, the glue or instant adhesive solidifies. This is adhesion—the process of transitioning from a liquid to a solid, and it is suitable for applications where the bond must not come apart.

What is Pressure-Sensitive Adhesion?

Picture the adhesive side of cellophane tape or packaging tape. These tapes maintain their soft and sticky texture before and after they are applied. This is pressure-sensitive adhesion—when the adhesive has both liquid and solid properties and does not undergo a state change. A main difference between pressure-sensitive adhesives and adhesives is their ability to be peeled off and reapplied after application.

Adhesives and pressure-sensitive adhesives have distinct qualities, each used for different applications to leverage their respective features.

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