In
polymer chemistry
Polymer chemistry is a sub-discipline of chemistry that focuses on the structures, chemical synthesis, and chemical and physical properties of polymers and macromolecules. The principles and methods used within polymer chemistry are also applic ...
, the gel point is an abrupt change in the
viscosity
Viscosity is a measure of a fluid's rate-dependent drag (physics), resistance to a change in shape or to movement of its neighboring portions relative to one another. For liquids, it corresponds to the informal concept of ''thickness''; for e ...
of a solution containing polymerizable components. At the gel point, a solution undergoes
gelation
In polymer chemistry, gelation (gel transition) is the formation of a gel from a system with polymers. Branched polymers can form links between the chains, which lead to progressively larger polymers. As the linking continues, larger branched p ...
, as reflected in a loss in fluidity. After the monomer/polymer solution has passed the gel point, internal stress builds up in the gel phase, which can lead to volume shrinkage. Gelation is characteristic of polymerizations that include
crosslinkers that can form 2- or 3-dimensional networks. For example, the condensation of a
dicarboxylic acid
In organic chemistry, a dicarboxylic acid is an organic compound containing two carboxyl groups (). The general molecular formula for dicarboxylic acids can be written as , where R can be aliphatic or aromatic.Boy Cornils, Peter Lappe "Dicarbox ...
and a
triol
In chemistry, a triol is an organic compound containing three hydroxyl groups ( functional groups),diol
A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol may also be called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified. They are used as protecting gro ...
will not. The gel is often a small percentage of the mixture, even though it greatly influences the properties of the bulk.
Mathematical definition
An infinite
polymer network
In polymer chemistry, branching is the regular or irregular attachment of side chains to a polymer's backbone chain. It occurs by the replacement of a substituent (e.g. a hydrogen atom) on a monomer subunit by another covalently-bonded chain ...
appears at the gel point. Assuming that it is possible to measure the extent of reaction,
, defined as the fraction of
monomer
A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization.
Classification
Chemis ...
s that appear in
cross-link
In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
s, the gel point can be determined.
The critical extent of reaction
for the gel point to be formed is given by:
:
For example, a polymer with N≈200 is able to reach the gel point with only 0.5% of monomers reacting. This shows the ease at which polymers are able to form infinite networks.
The critical extent of reaction for
gelation
In polymer chemistry, gelation (gel transition) is the formation of a gel from a system with polymers. Branched polymers can form links between the chains, which lead to progressively larger polymers. As the linking continues, larger branched p ...
can be determined as a function of the properties of the monomer mixture,
,
, and
:
:
See also
*
Pour point
The pour point of a liquid is the temperature below which the liquid loses its flow characteristics.
It is defined as the minimum temperature in which the oil has the ability to pour down from a beaker. In crude oil a high pour point is generally ...
*
Cold filter plugging point
Cold is the presence of low temperature, especially in the atmosphere. In common usage, cold is often a subjective perception. A lower bound to temperature is absolute zero, defined as 0.00K on the Kelvin scale, an absolute thermodynamic ...
*
Petroleum
Petroleum, also known as crude oil or simply oil, is a naturally occurring, yellowish-black liquid chemical mixture found in geological formations, consisting mainly of hydrocarbons. The term ''petroleum'' refers both to naturally occurring un ...
References
Further reading
*{{cite book, author1=Rudin, Alfred , author2=Choi, Phillip , title=The Elements of Polymer Science and Engineering, 3rd Edition, year=2012, publisher=Elsevier Science, page=410, isbn=978-0-12-382178-2
Polymer physics
Chemical properties