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In the
physical sciences Physical science is a branch of natural science Natural science is a branch A branch ( or , ) or tree branch (sometimes referred to in botany Botany, also called , plant biology or phytology, is the science of plant life and a b ...
, 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 250px, STM image of a self-assembled_supramolecular.html" ;"title="self-assembly.html" ;"title="adsorbate.html" ;"title="quinacridone adsorbate">quinacridone adsorbate. The self-assembly">self-assembled supramolecular">self-assembly.html" ;"ti ...

surface science
. In
thermal equilibrium Two physical system A physical system is a collection of physical objects. In physics, it is a portion of the physical universe chosen for analysis. Everything outside the system is known as the environment (systems), environment. The enviro ...

thermal equilibrium
, the regions in contact are called phases, and the interface is called a
phase boundary In thermal equilibrium, each phase (i.e. liquid A liquid is a nearly incompressible fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. Flu ...
. An example for an interface out of equilibrium is the
grain boundary of a polycrystalline A crystallite is a small or even microscopic crystal A crystal or crystalline solid is a solid material whose constituents (such as atoms, molecules, or ions) are arranged in a highly ordered microscopic structure, for ...
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 chemistry, a mixture is a material made up of two or more different chemical substances which are not chemically combined. A mixture is the physical combination of two or more substances in which the identities are r ...

colloid
s. Interfaces can be flat or curved. For example,
oil An oil is any nonpolar In chemistry Chemistry is the science, scientific study of the properties and behavior of matter. It is a natural science that covers the Chemical element, elements that make up matter to the chemical compound ...

oil
droplets in a
salad dressing A salad is a dish consisting of mixed pieces of food Food is any substance consumed to provide nutritional support for an organism In biology, an organism (from Ancient Greek, Greek: ὀργανισμός, ''organismos'') is any ...

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 A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physi ...

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 Surface tension is the tendency of liquid A liquid is a nearly incompressible In fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physi ...

surface tension
tends to keep the meniscus flat, while the
disjoining pressureDisjoining pressure (symbol Πd), in surface chemistry 250px, STM image of a self-assembled_supramolecular.html" ;"title="self-assembly.html" ;"title="adsorbate.html" ;"title="quinacridone adsorbate">quinacridone adsorbate. The self-assembly">se ...

disjoining pressure
makes the film conformal to the substrate. The equilibrium meniscus shape is a result of the competition between the
capillary pressureIn fluid statics Fluid statics or hydrostatics is the branch of fluid mechanics that studies "fluids at hydrostatic equilibrium and the pressure in a fluid or exerted by a fluid on an immersed body". It encompasses the study of the conditions u ...
and
disjoining pressureDisjoining pressure (symbol Πd), in surface chemistry 250px, STM image of a self-assembled_supramolecular.html" ;"title="self-assembly.html" ;"title="adsorbate.html" ;"title="quinacridone adsorbate">quinacridone adsorbate. The self-assembly">se ...

disjoining pressure
. Interfaces may cause various
optical phenomena Optical phenomena are any observable events that result from the interaction of light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the huma ...
, such as
refraction In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force ...

refraction
.
Optical lenses
Optical lenses
serve as an example of a practical application of the interface between
glass Glass is a non- crystalline, often transparency and translucency, 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 ...

glass
and air. One topical interface system is the gas-liquid interface between
aerosols An aerosol (abbreviation of "aero-solution") is a suspension Suspension or suspended may refer to: Science and engineering * Suspension (topology), in mathematics * Suspension (dynamical systems), in mathematics * Suspension of a ring, in mathe ...
and other atmospheric molecules.


See also

*
Capillary surfaceIn fluid mechanics Fluid mechanics is the branch of physics concerned with the mechanics Mechanics (Ancient Greek, Greek: ) is the area of physics concerned with the motions of physical objects, more specifically the relationships among force ...
, a surface that represents the boundary between two fluids *
Disjoining pressureDisjoining pressure (symbol Πd), in surface chemistry 250px, STM image of a self-assembled_supramolecular.html" ;"title="self-assembly.html" ;"title="adsorbate.html" ;"title="quinacridone adsorbate">quinacridone adsorbate. The self-assembly">se ...

Disjoining pressure
*
Free surface In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

Free surface
*
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 Tissue (biology), tissues formed by layers of cells * ...
*
Surface phenomenon Surface science is the study of physical Physical may refer to: *Physical examination, a regular overall check-up with a doctor *Physical (album), ''Physical'' (album), a 1981 album by Olivia Newton-John **Physical (Olivia Newton-John song), "Ph ...


References

Colloidal chemistry Matter Surface science {{Chem-stub