Cohesion (chemistry)

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Cohesion (chemistry)

Cohesion (n. lat. cohaerere "stick or stay together") or cohesive attraction or cohesive force is a physical property

Physical property

A physical property is any aspect of an object or substance that can be measurement or perception without changing its Identity . Physical properties can be Intensive and extensive properties....
of a substance, caused by the intermolecular attraction between like-molecules within a body or substance that acts to unite them.

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Encyclopedia

Cohesion (n. lat. cohaerere "stick or stay together") or cohesive attraction or cohesive force is a physical property

Physical property

Water

Water is a common chemical substance that is essential for the survival of all known forms of life. In typical usage, water refers only to its liquid form or States of matter, but the substance also has a solid state, ice, and a gaseous state, water vapor or steam....
, for example, is strongly cohesive as each molecule may make four hydrogen bonds to other water molecules in a tetrahedral configuration. This results in a relatively strong Coulomb force between molecules. Van der Waals gases

Van der Waals equation

The 'van der Waals equation' is an equation of state for a fluid composed of particles that have a non-zero size and a pairwise attractive inter-particle force It was derived by Johannes Diderik van der Waals in 1873, based on a modification of the ideal gas law, who received the Nobel prize in 1910 for "his work on the equation of state for...
such as methane

Methane

Methane is a chemical compound with the molecular formula . It is the simplest alkane, and the principal component of natural gas. Methane's bond angles are 109.5 degrees....
, however, have weak cohesion due only to Van der Waals forces that operate by induced polarity in non-polar molecules.

Cohesion, along with adhesion

Adhesion

Adhesion is the tendency of certain dissimilar molecules to cling together due to attractive forces....
(attraction between unlike molecules), helps explain phenomena such as surface tension

Surface tension

Surface tension is an attractive property of the surface of a liquid. It is what causes the surface portion of liquid to be attracted to another surface, such as that of another portion of liquid ....
and capillary action

Capillary action

Capillary action, capillarity, capillary motion, or wicking refers to two phenomena:# The movement of liquids in thin tubes...
.

Industry applications

The construction

Construction

In the fields of architecture and civil engineering, construction is a process that consists of the building or assembling of infrastructure. Far from being a single activity, large scale construction is a feat of multitasking....
industry uses many materials that undergo a phase transition

Phase transition

In thermodynamics, a phase transition is the transformation of a thermodynamic system from one phase to another.At phase-transition point, physical properties may undergo abrupt change- for instance, volume of the two phases may be vastly different....
during installation and use. These include, but are not limited to the following:

caulking
Caulking

Caulking is a Process used to seal the seams in wooden boats or ships, and riveted iron or steel ships, in order to make them watertight. The same term also refers to the application of flexible sealing compounds to close up crevices in structures against water, air, dust, insects, or as a component in firestopping....
firestop mortar
Mortar (firestop)

Firestop mortars are most typically used to firestop large openings in walls and floors required to have a fire-resistance rating. They are passive fire protection items....
concrete
Concrete

Concrete is a construction material composed of cement as well as other cementitious materials such as fly ash and slag cement, construction aggregate , water , and Chemistry admixtures....
plaster
Plaster

The term plaster can refer to plaster of Paris, lime plaster, or cement plaster. This article deals mainly with plaster of Paris.Plaster of Paris is a type of building material based on calcium sulfate Hydrate, nominally CaSO4?0.5H2O....
spray fireproofing
Fireproofing

Fireproofing, a passive fire protection measure, refers to the act of making materials or building more resistant to fire, or to those materials themselves, or the act of applying such materials....
paint
Paint

Paint is any liquid, liquifiable, or mastic composition which after application to a Substrate in a thin layer is converted to an opaque solid film....

Often, these building material

Building material

Building material is any raw material which is used for a construction purpose. Many naturally occurring substances, such as clay, sand, wood and rocks, even twigs and leaves have been used to construct buildings....
s are required not just to be cast and occupy space. They must also stick and maintain a certain thickness or space. Paint typically does not require as much cohesion as caulking, as paint is applied much more thinly. High quality firestop mortars require extreme cohesion with the adhesion because they are often used in large wall openings, where the mortar must not only adhere to adjacent materials but also hold itself up, forming a wall in the plastic state, which must hold long enough to cure and convert to the solid state. The thicker the application, the more cohesion is required.

External links

(Audio slideshow from the National High Magnetic Field Laboratory explaining cohesion, surface tension and hydrogen bonds)

Cohesion (chemistry)

Industry applications

See also

External links