In the
physical sciences
Physical science is a branch of natural science that studies non-living systems, in contrast to life science. It in turn has many branches, each referred to as a "physical science", together called the "physical sciences".
Definition
Phy ...
, an interface is the boundary between two spatial regions occupied by different matter, or by matter in different physical states. The interface between matter and air, or matter and vacuum, is called a surface, and studied in
surface science. In
thermal equilibrium
Two physical systems are in thermal equilibrium if there is no net flow of thermal energy between them when they are connected by a path permeable to heat. Thermal equilibrium obeys the zeroth law of thermodynamics. A system is said to be i ...
, the regions in contact are called
phases, and the interface is called a
phase boundary. An example for an interface out of equilibrium is the
grain boundary
In materials science, a grain boundary is the interface between two grains, or crystallites, in a polycrystalline material. Grain boundaries are two-dimensional defects in the crystal structure, and tend to decrease the electrical and thermal ...
in polycrystalline matter.
The importance of the interface depends on the type of system: the bigger the quotient area/volume, the greater the effect the interface will have. Consequently, interfaces are very important in systems with large interface area-to-volume ratios, such as
colloids.
Interfaces can be flat or curved. For example,
oil
An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) & lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturated ...
droplets in a
salad dressing
A salad dressing is a sauce for salads. Used on virtually all '' leafy salads'', dressings may also be used in making salads of beans (such as three bean salad), noodle or pasta salads and antipasti, and forms of potato salad.
Salad dressing ...
are spherical but the interface between water and air in a glass of water is mostly flat.
Surface tension is the physical property which rules interface processes involving liquids. For a liquid film on flat surfaces, the liquid-vapor interface keeps flat to minimize interfacial area and system
free energy. For a liquid film on rough surfaces, the
surface tension tends to keep the
meniscus
Meniscus may refer to:
*Meniscus (anatomy), crescent-shaped fibrocartilaginous structure that partly divides a joint cavity
*Meniscus (liquid)
The meniscus (plural: ''menisci'', from the Greek for "crescent") is the curve in the upper surface ...
flat, while the
disjoining pressure
In surface chemistry, disjoining pressure (symbol ) according to an IUPAC definition arises from an attractive interaction between two surfaces. For two flat and parallel surfaces, the value of the disjoining pressure (i.e., the force per unit ar ...
makes the film conformal to the substrate. The equilibrium meniscus shape is a result of the competition between the
capillary pressure and
disjoining pressure
In surface chemistry, disjoining pressure (symbol ) according to an IUPAC definition arises from an attractive interaction between two surfaces. For two flat and parallel surfaces, the value of the disjoining pressure (i.e., the force per unit ar ...
.
Interfaces may cause various
optical phenomena
Optical phenomena are any observable events that result from the interaction of light and matter.
All optical phenomena coincide with quantum phenomena. Common optical phenomena are often due to the interaction of light from the sun or moon with ...
, such as
refraction
In physics, refraction is the redirection of a wave as it passes from one medium to another. The redirection can be caused by the wave's change in speed or by a change in the medium. Refraction of light is the most commonly observed phenome ...
.
Optical lenses serve as an example of a practical application of the interface between
glass
Glass is a non-crystalline, often transparent, amorphous solid that has widespread practical, technological, and decorative use in, for example, window panes, tableware, and optics. Glass is most often formed by rapid cooling ( quenching ...
and air.
One topical interface system is the gas-liquid interface between
aerosols and other atmospheric molecules.
See also
*
Capillary surface
In fluid mechanics and mathematics, a capillary surface is a surface that represents the interface between two different fluids. As a consequence of being a surface, a capillary surface has no thickness in slight contrast with most real fluid inte ...
, a surface that represents the boundary between two fluids
*
Disjoining pressure
In surface chemistry, disjoining pressure (symbol ) according to an IUPAC definition arises from an attractive interaction between two surfaces. For two flat and parallel surfaces, the value of the disjoining pressure (i.e., the force per unit ar ...
*
Free surface
In physics, a free surface is the surface of a fluid that is subject to zero parallel shear stress,
such as the interface between two homogeneous fluids.
An example of two such homogeneous fluids would be a body of water (liquid) and the air in ...
*
Interface and colloid science
Interface and colloid science is an interdisciplinary intersection of branches of chemistry, physics, nanoscience and other fields dealing with colloids, heterogeneous systems consisting of a mechanical mixture of particles between 1 nm and ...
*
Membrane (disambiguation) Membrane most commonly means a thin, selective barrier, but it is sometimes used for films that function as separators, like biological membranes. Membrane may also refer to:
Biology:
* Isolating tissues formed by layers of cells
** Amnion, a memb ...
*
Surface phenomenon
References
Colloidal chemistry
Matter
Surface science
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