interfacial

Interfacial refers to anything relating to an interface, the boundary between two materials or phases with distinct properties. Interfaces can separate immiscible liquids, such as oil and water; involve a solid in contact with a liquid or gas; or occur between two solids. The study of interfacial phenomena is central to surface science, colloid and interface science, materials science, chemistry, and biology.

A key concept is interfacial tension (also called interfacial energy), the excess free energy per unit area at an interface. Interfacial tension drives the tendency to minimize interfacial area and underpins processes such as droplet formation, wetting, spreading, and capillarity. Wetting is described by the contact angle formed by a liquid at a solid surface, which reflects the balance of interfacial tensions among the three phases.

Transport and chemical activity at interfaces are often distinct from the bulk. Diffusion and convection can be enhanced or hindered across interfaces, and adsorption of molecules to the interface can alter physical properties. Reactions can occur specifically at interfaces, including electrochemical reactions at electrode–electrolyte interfaces or catalytic reactions at solid–gas or solid–liquid boundaries.

Measurement and characterization methods include tensiometry to quantify interfacial tension, and interfacial rheology to probe viscoelastic properties of interfacial layers. Other techniques examine interfacial structure and dynamics, such as microscopy and spectroscopy of interfacial films.

Applications span emulsions and foams stabilization, coatings and corrosion protection, membranes and separations, and energy conversion devices where interface properties govern performance. In biology, interfacial concepts help describe cell membranes and other boundary layers that control transport and signaling.