Interface (chemistry)

As an interface or phase boundary surface between the two phases is called in physics and materials science, for example, the interface between two immiscible liquids such as oil and water.

As interfaces in the strict sense only the following areas are designated:

• Between liquid and liquid phases
• Between liquid and solid phases
• Between solid and solid phases,

While the surface

• Between solid and gaseous phases

Is usually referred to as a surface.

The distinction between interfaces and surfaces is historical and partly arbitrary. The fact that the third above-mentioned case ( interfaces within a solid body ) has the meaning shown by the numerous discontinuities in the crust and mantle.

With the properties of interfaces in a broader sense to deal the surface chemistry and surface physics.

Interfacial and surface

A surface can be less clearly defined than one might assume. The geometric definition as a whole of the surfaces that define a body from the outside, will be problematic from the microscopic range. The " surface atoms " are not sharply defined and balls between them may be gaps that can be greater by much than the atoms themselves, the size of a " boundary or surface " is scale- dependent, so depending on the observation scale used.

Therefore, a distinction between external and internal surface at all porous materials is given: This form considered "outside" a compact body, but are filled with numerous cavities. For various physical and chemical processes, these inner surfaces are, however, just as relevant as the outer surface. The inside surface often exceeds the outer many orders of magnitude.

Typical examples are:

• On Earth in particular the Earth's surface and the water level of the sea and waters
• Stars in the solar photosphere
• The free surface of a liquid under gas pressure
• , noted in the art, the surface to be machined of a workpiece as a deviation from the ideal shape in the body surface indicating
• A thin layer on an object, see also surface treatment ( coating )
• The measure of powder, piles and the like, the specific surface as total volume or mass related surface
• Body surface of man, estimation formulas for scale-dependent size

Basics

Within a phase interacting atoms or molecules in all directions with atoms or molecules in their neighborhood. Here acting in all directions same interaction forces ( cohesions ). In the vicinity of the interface, this is not the case. At the interface are in the direction of the neighboring phase may have no or only very different neighbors for interaction available. For atoms or molecules it is energetically unfavorable in general, to be in the vicinity of the interface. This results in a surface tension, in the case of liquid-gas surface tension.

• Surface active substances such as surfactants (emulsifiers ) to reduce the interfacial tension and promote the mixing of two phases to form an emulsion or dispersion.

• At the interface between solid and gaseous phase, it generally comes to an adsorption of substances from the gas phase. This phenomenon is utilized in many industrial processes, and plays a role in the heterogeneous catalysis.

• An electrochemical double layer is formed at the phase boundary between an electron conductor ( solid) and an electrolyte ( liquid). This double layer is an important phenomenon of electrochemistry.

Phase boundary in the phase diagram

The phase boundary is shown by the phase boundary in dependence on temperature and kinetic pressure in the phase diagram of a substance. This behavior is typical for the material property.

Interface in audio engineering

See the pressure congestion at boundary microphone.