Material Surface and Interface Fundamentals
Materials science, information science and the life sciences are the three frontiers of today’s new technological revolution, and the surface and interface of materials occupy an important position in materials science.
What are surfaces and interfaces? The objects studied by surface and interface science are inhomogeneous systems with multiple phases — that is, systems in which two or more phases of different properties exist. As the editors of this aluminate coupling agent article explain, the surface/interface is the transition region from one phase to another.
Depending on the state of aggregation of the matter, surfaces and interfaces are usually classified into the following five types:
Solid–Gas | Liquid–Gas | Solid–Liquid | Liquid–Liquid | Solid–Solid
A gas and a gas always form a homogeneous system, so no surface/interface exists between them. By convention, the transition regions of solid–gas and liquid–gas are called surfaces, while those of solid–liquid, liquid–liquid and solid–solid are called interfaces.
In reality, there is no sharply defined dividing surface between two phases; the transition from one phase to another is gradual. The structure, energy and composition of the surface/interface region change in a continuous gradient. The surface/interface is therefore not a geometrical plane but a quasi-three-dimensional region of complex structure about several molecular diameters thick. For this reason the interface region is often treated as a phase or layer, known as the interface phase or interface layer.
The surface of a material differs markedly from its interior bulk, both in structure and in chemical composition. This is because the atoms inside a material are acted on equally by the surrounding atoms, whereas the atoms at the surface experience an unbalanced force field, giving rise to surface energy.
In a material composed of different components, interfaces can form between the components, and a given component may also become enriched at the surface/interface of the material. Even in a single-component material, internal defects such as dislocations, or the formation of grain boundaries due to differences in crystallinity, can create interfaces within the material. The surface and interface of a material have a decisive influence on its overall properties: corrosion, ageing, hardening, failure, printing, film coating, adhesion, compounding and so on are all closely related to the surface and interface of the material.
The study of surface and interface phenomena is therefore of great significance.
