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 is called the "physical sciences".
Definition
...
, an interface is the boundary between two spatial regions occupied by different
matter
In classical physics and general chemistry, matter is any substance that has mass and takes up space by having volume. All everyday objects that can be touched are ultimately composed of atoms, which are made up of interacting subatomic pa ...
, 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, 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
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
colloid
A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others exte ...
s.
Interfaces can be flat or curved. For example,
oil droplets in a
salad dressing are spherical but the interface between water and air in a glass of water is mostly flat.
Surface tension
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...
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
Surface tension is the tendency of liquid surfaces at rest to shrink into the minimum surface area possible. Surface tension (physics), tension is what allows objects with a higher density than water such as razor blades and insects (e.g. Ge ...
tends to keep the
meniscus flat, while the
disjoining pressure makes the film conformal to the substrate. The equilibrium meniscus shape is a result of the competition between the
capillary pressure and disjoining pressure.
Interfaces may cause various
optical phenomena, such as
refraction
In physics, refraction is the redirection of a wave as it passes from one transmission medium, 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 commo ...
.
Optical lenses serve as an example of a practical application of the interface between
glass
Glass is an amorphous (non-crystalline solid, non-crystalline) solid. Because it is often transparency and translucency, transparent and chemically inert, glass has found widespread practical, technological, and decorative use in window pane ...
and air.
One topical interface system is the gas-liquid interface between
aerosols and other atmospheric molecules.
See also
*
Capillary surface, a surface that represents the boundary between two fluids
*
Disjoining pressure
*
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
*
Membrane
*
Surface phenomenon
References
Colloidal chemistry
Matter
Surface science
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