Adhesion

Adhesion is the attraction between unlike substances at an interface, enabling two materials to stick together. It arises from chemical bonds, electrostatic forces, van der Waals interactions, and mechanical interlocking, and it is influenced by surface chemistry and morphology.

It is distinct from cohesion, the attraction between similar molecules within a material. Adhesion concerns the interface between dissimilar materials, coatings, or layers, and determines bond strength and durability.

Mechanisms include ionic or covalent bonding, hydrogen bonding, van der Waals forces, and electrostatic interactions, as well as physical interlocking with surface roughness. Wetting and contact angle affect adhesion quality.

Factors affecting adhesion include substrate surface energy, cleanliness, roughness, moisture, temperature, curing or setting conditions, and adhesive-substrate compatibility. Environmental exposure can degrade bonds over time.

Types range from natural adhesives (plant resins, mucus) to synthetic systems (epoxies, polyurethanes, cyanoacrylates, silicones). Applications span packaging, electronics, construction, medical devices, dental bonding, and wound closure; bioadhesive research seeks reversible and biocompatible options.