
A colloid is a
mixture
In chemistry, a mixture is a material made up of two or more different chemical substances which can be separated by physical method. It is an impure substance made up of 2 or more elements or compounds mechanically mixed together in any proporti ...
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
Liquid is a state of matter with a definite volume but no fixed shape. Liquids adapt to the shape of their container and are nearly incompressible, maintaining their volume even under pressure. The density of a liquid is usually close to th ...
,
while others extend the definition to include substances like
aerosol
An aerosol is a suspension (chemistry), suspension of fine solid particles or liquid Drop (liquid), droplets in air or another gas. Aerosols can be generated from natural or Human impact on the environment, human causes. The term ''aerosol'' co ...
s and
gels. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word ''
suspension'' is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1
nanometre to 1
micrometre
The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
.
Some colloids are
translucent because of the
Tyndall effect, which is the
scattering
In physics, scattering is a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiat ...
of light by particles in the colloid. Other colloids may be
opaque or have a slight color.
Colloidal suspensions are the subject of
interface and colloid science. This field of study began in 1845 by
Francesco Selmi, who called them pseudosolutions, and expanded by
Michael Faraday
Michael Faraday (; 22 September 1791 – 25 August 1867) was an English chemist and physicist who contributed to the study of electrochemistry and electromagnetism. His main discoveries include the principles underlying electromagnetic inducti ...
and
Thomas Graham, who coined the term ''colloid'' in 1861.
Classification
Colloids can be classified as follows:
Homogeneous mixtures with a dispersed phase in this size range may be called ''colloidal aerosols'', ''colloidal emulsions'', ''colloidal suspensions'', ''colloidal foams'', ''colloidal dispersions'', or ''hydrosols''.
File:Aerogel hand.jpg, Aerogel
File:Jello Cubes.jpg, Jello cubes
File:Opaleszens Kolloid SiO2.jpg, Colloidal silica gel with light opalescence
File:Crème Chantilly.jpg, Whipped cream
File:Dollop of hair gel.jpg, A dollop of hair gel
File:Cream in round container.jpg, Creams are semi-solid emulsions of oil and water. Oil-in-water creams are used for cosmetic purpose while water-in-oil creams for medicinal purpose
File:Why is the sky blue.jpg, Tyndall effect in an opalite:
it scatters blue light making it appear blue from the side, but orange light shines through.
Opal
Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...
is a gel in which water is dispersed in silica crystals.
File:Glass of Milk (33657535532).jpg, Milk
Milk is a white liquid food produced by the mammary glands of lactating mammals. It is the primary source of nutrition for young mammals (including breastfeeding, breastfed human infants) before they are able to digestion, digest solid food. ...
- emulsion of liquid butterfat globules dispersed in water
File:Mist - Ensay region3.jpg, Mist
Hydrocolloids
Hydrocolloids describe certain
chemicals (mostly
polysaccharides
Polysaccharides (), or polycarbohydrates, are the most abundant carbohydrates found in food. They are long-chain polymeric carbohydrates composed of monosaccharide units bound together by glycosidic linkages. This carbohydrate can react with wat ...
and
proteins
Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residues. Proteins perform a vast array of functions within organisms, including catalysing metabolic reactions, DNA replication, re ...
) that are colloidally dispersible in
water
Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...
. Thus becoming effectively "soluble" they change the
rheology of water by raising the viscosity and/or inducing gelation. They may provide other interactive effects with other chemicals, in some cases synergistic, in others antagonistic. Using these attributes hydrocolloids are very useful chemicals since in many areas of technology from
foods through
pharmaceuticals, personal care and industrial applications, they can provide stabilization, destabilization and separation, gelation, flow control, crystallization control and numerous other effects. Apart from uses of the soluble forms some of the hydrocolloids have additional useful functionality in a dry form if after solubilization they have the water removed - as in the formation of films for breath strips or sausage casings or indeed, wound dressing fibers, some being more compatible with
skin
Skin is the layer of usually soft, flexible outer tissue covering the body of a vertebrate animal, with three main functions: protection, regulation, and sensation.
Other animal coverings, such as the arthropod exoskeleton, have different ...
than others. There are many different types of hydrocolloids each with differences in structure function and utility that generally are best suited to particular application areas in the control of rheology and the physical modification of form and texture. Some hydrocolloids like starch and casein are useful foods as well as rheology modifiers, others have limited nutritive value, usually providing a source of fiber.
The term hydrocolloids also refers to
a type of dressing designed to lock moisture in the skin and help the natural healing process of skin to reduce scarring, itching and soreness.
Components
Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) and gelatin. They are normally combined with some type of sealant, i.e. polyurethane to 'stick' to the skin.
Compared with solution
A colloid has a
dispersed phase and a continuous phase, whereas in a
solution, the
solute and
solvent constitute only one phase. A solute in a solution are individual
molecule
A molecule is a group of two or more atoms that are held together by Force, attractive forces known as chemical bonds; depending on context, the term may or may not include ions that satisfy this criterion. In quantum physics, organic chemi ...
s or
ions, whereas colloidal particles are bigger. For example, in a solution of salt in water, the
sodium chloride
Sodium chloride , commonly known as Salt#Edible salt, edible salt, is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. It is transparent or translucent, brittle, hygroscopic, and occurs a ...
(NaCl)
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, forming a crystal lattice that extends in all directions. In addition, macros ...
dissolves, and the Na
+ and Cl
− ions are surrounded by water molecules. However, in a colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution.
Interaction between particles
The following forces play an important role in the interaction of colloid particles:
*
Excluded volume repulsion: This refers to the impossibility of any overlap between hard particles.
*
Electrostatic interaction: Colloidal particles often carry an electrical charge and therefore attract or repel each other. The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.
*
van der Waals forces: This is due to interaction between two dipoles that are either permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a temporary dipole in a particle. This temporary dipole induces a dipole in particles nearby. The temporary dipole and the induced dipoles are then attracted to each other. This is known as van der Waals force, and is always present (unless the refractive indexes of the dispersed and continuous phases are matched), is short-range, and is attractive.
*
Steric forces: A repulsive steric force typically occurring due to adsorbed polymers coating a colloid's surface.
*
Depletion forces: An attractive entropic force arising from an osmotic pressure imbalance when colloids are suspended in a medium of much smaller particles or polymers called depletants.
Sedimentation velocity

The Earth’s
gravitational field
In physics, a gravitational field or gravitational acceleration field is a vector field used to explain the influences that a body extends into the space around itself. A gravitational field is used to explain gravitational phenomena, such as ...
acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will
sediment
Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...
(fall to the bottom), or if they are less dense, they will
cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller
Brownian motion to counteract this movement.
The sedimentation or creaming velocity is found by equating the
Stokes drag force with the
gravitational force:
:
where
:
is the
Archimedean weight of the colloidal particles,
:
is 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 the suspension medium,
:
is the
radius
In classical geometry, a radius (: radii or radiuses) of a circle or sphere is any of the line segments from its Centre (geometry), center to its perimeter, and in more modern usage, it is also their length. The radius of a regular polygon is th ...
of the colloidal particle,
and
is the sedimentation or creaming velocity.
The mass of the colloidal particle is found using:
:
where
:
is the volume of the colloidal particle, calculated using the volume of a sphere
,
and
is the difference in mass density between the colloidal particle and the suspension medium.
By rearranging, the sedimentation or creaming velocity is:
:
There is an upper size-limit for the diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension.
The colloidal particles are said to be in
sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion.
Preparation
There are two principal ways to prepare colloids:
*
Dispersion of large particles or droplets to the colloidal dimensions by
milling,
spraying, or application of shear (e.g., shaking, mixing, or
high shear mixing).
* Condensation of small dissolved molecules into larger colloidal particles by
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
,
condensation, or
redox
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...
reactions. Such processes are used in the preparation of colloidal
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
or
gold
Gold is a chemical element; it has chemical symbol Au (from Latin ) and atomic number 79. In its pure form, it is a brightness, bright, slightly orange-yellow, dense, soft, malleable, and ductile metal. Chemically, gold is a transition metal ...
.
Stabilization
The stability of a colloidal system is defined by particles remaining suspended in solution and depends on the interaction forces between the particles. These include electrostatic interactions and
van der Waals forces
In molecular physics and chemistry, the van der Waals force (sometimes van der Waals' force) is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical ele ...
, because they both contribute to the overall
free energy of the system.
A colloid is stable if the interaction energy due to attractive forces between the colloidal particles is less than
kT, where k is the
Boltzmann constant and T is the
absolute temperature. If this is the case, then the colloidal particles will repel or only weakly attract each other, and the substance will remain a suspension.
If the interaction energy is greater than kT, the attractive forces will prevail, and the colloidal particles will begin to clump together. This process is referred to generally as
aggregation, but is also referred to as
flocculation
In colloidal chemistry, flocculation is a process by which colloidal particles come out of Suspension (chemistry), suspension to sediment in the form of floc or flake, either spontaneously or due to the addition of a clarifying agent. The actio ...
,
coagulation or
precipitation
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, rain and snow mixed ("sleet" in Commonwe ...
. While these terms are often used interchangeably, for some definitions they have slightly different meanings. For example, coagulation can be used to describe irreversible, permanent aggregation where the forces holding the particles together are stronger than any external forces caused by stirring or mixing. Flocculation can be used to describe reversible aggregation involving weaker attractive forces, and the aggregate is usually called a ''floc''. The term precipitation is normally reserved for describing a phase change from a colloid dispersion to a solid (precipitate) when it is subjected to a perturbation.
Aggregation causes sedimentation or creaming, therefore the colloid is unstable: if either of these processes occur the colloid will no longer be a suspension.

Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation.
* Electrostatic stabilization is based on the mutual repulsion of like electrical charges. The charge of colloidal particles is structured in an
electrical double layer, where the particles are charged on the surface, but then attract counterions (ions of opposite charge) which surround the particle. The electrostatic repulsion between suspended colloidal particles is most readily quantified in terms of the
zeta potential. The combined effect of van der Waals attraction and electrostatic repulsion on aggregation is described quantitatively by the
DLVO theory. A common method of stabilising a colloid (converting it from a precipitate) is
peptization, a process where it is shaken with an electrolyte.
* Steric stabilization consists absorbing a layer of a polymer or surfactant on the particles to prevent them from getting close in the range of attractive forces.
The polymer consists of chains that are attached to the particle surface, and the part of the chain that extends out is soluble in the suspension medium. This technique is used to stabilize colloidal particles in all types of solvents, including organic solvents.
A combination of the two mechanisms is also possible (electrosteric stabilization).

A method called gel network stabilization represents the principal way to produce colloids stable to both aggregation and sedimentation. The method consists in adding to the colloidal suspension a polymer able to form a gel network. Particle settling is hindered by the stiffness of the polymeric matrix where particles are trapped,
and the long polymeric chains can provide a steric or electrosteric stabilization to dispersed particles. Examples of such substances are
xanthan
Xanthan gum () is a polysaccharide with many industrial uses, including as a common food additive. It is an effective thickening agent and stabilizer (food), stabilizer that prevents ingredients from separating. It can be produced from monosaccha ...
and
guar gum
Guar gum, also called guaran, is a galactomannan polysaccharide extracted from guar beans that has thickening and stabilizing properties useful in food, feed, and industrial applications. The guar seeds are mechanically dehusked, hydrated, mi ...
.
Destabilization
Destabilization can be accomplished by different methods:
*Removal of the electrostatic barrier that prevents aggregation of the particles. This can be accomplished by the addition of salt to a suspension to reduce the
Debye screening length (the width of the electrical double layer) of the particles. It is also accomplished by changing the pH of a suspension to effectively neutralise the surface charge of the particles in suspension.
This removes the repulsive forces that keep colloidal particles separate and allows for aggregation due to van der Waals forces. Minor changes in pH can manifest in significant alteration to the
zeta potential. When the magnitude of the zeta potential lies below a certain threshold, typically around ± 5mV, rapid coagulation or aggregation tends to occur.
*Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively charged colloidal silica or clay particles can be flocculated by the addition of a positively charged polymer.
*Addition of non-adsorbed polymers called
depletants that cause aggregation due to entropic effects.
Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions, wherein individual clusters of particles sediment if they are more dense than the suspension medium, or cream if they are less dense. However, colloidal suspensions of higher-volume fraction form colloidal gels with
viscoelastic
In materials science and continuum mechanics, viscoelasticity is the property of materials that exhibit both Viscosity, viscous and Elasticity (physics), elastic characteristics when undergoing deformation (engineering), deformation. Viscous mate ...
properties. Viscoelastic colloidal gels, such as
bentonite
Bentonite ( ) is an Absorption (chemistry), absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelli ...
and
toothpaste, flow like liquids under shear, but maintain their shape when shear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on the toothbrush after it is applied.
Monitoring stability

The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple
light scattering coupled with vertical scanning. This method, known as
turbidimetry, is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored. These phenomena are associated with unstable colloids.
Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles.
Accelerating methods for shelf life prediction
The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
Mechanical acceleration including vibration,
centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Segregation of different populations of particles have been highlighted when using centrifugation and vibration.
As a model system for atoms
In
physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
, colloids are an interesting model system for
atom
Atoms are the basic particles of the chemical elements. An atom consists of a atomic nucleus, nucleus of protons and generally neutrons, surrounded by an electromagnetically bound swarm of electrons. The chemical elements are distinguished fr ...
s. Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as
confocal microscopy
Confocal microscopy, most frequently confocal laser scanning microscopy (CLSM) or laser scanning confocal microscopy (LSCM), is an optical imaging technique for increasing optical resolution and contrast (vision), contrast of a micrograph by me ...
. Many of the forces that govern the structure and behavior of matter, such as excluded volume interactions or electrostatic forces, govern the structure and behavior of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to
model
A model is an informative representation of an object, person, or system. The term originally denoted the plans of a building in late 16th-century English, and derived via French and Italian ultimately from Latin , .
Models can be divided in ...
the behavior of a hard sphere colloidal suspension.
Phase transition
In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...
s in colloidal suspensions can be studied in real time using optical techniques,
and are analogous to phase transitions in liquids. In many interesting cases optical fluidity is used to control colloid suspensions.
Crystals
A colloidal crystal is a highly
ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear
analogous to their atomic or molecular counterparts. One of the finest
natural examples of this ordering phenomenon can be found in precious
opal
Opal is a hydrated amorphous form of silicon dioxide, silica (SiO2·''n''H2O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a ...
, in which brilliant regions of pure
spectral color
Color (or colour in English in the Commonwealth of Nations, Commonwealth English; American and British English spelling differences#-our, -or, see spelling differences) is the visual perception based on the electromagnetic spectrum. Though co ...
result from
close-packed domains of
amorphous
In condensed matter physics and materials science, an amorphous solid (or non-crystalline solid) is a solid that lacks the long-range order that is a characteristic of a crystal. The terms "glass" and "glassy solid" are sometimes used synonymousl ...
colloidal spheres of
silicon dioxide
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundan ...
(or
silica
Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , commonly found in nature as quartz. In many parts of the world, silica is the major constituent of sand. Silica is one of the most complex and abundant f ...
, SiO
2). These spherical particles
precipitate in highly
siliceous pools in
Australia
Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...
and elsewhere, and form these highly ordered arrays after years of
sedimentation and
compression under
hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of
interstitial voids, which act as a natural
diffraction grating
In optics, a diffraction grating is an optical grating with a periodic structure that diffraction, diffracts light, or another type of electromagnetic radiation, into several beams traveling in different directions (i.e., different diffractio ...
for
visible light
Light, visible light, or visible radiation is electromagnetic radiation that can be visual perception, perceived by the human eye. Visible light spans the visible spectrum and is usually defined as having wavelengths in the range of 400– ...
wave
In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from List of types of equilibrium, equilibrium) of one or more quantities. ''Periodic waves'' oscillate repeatedly about an equilibrium ...
s, particularly when the interstitial spacing is of the same
order of magnitude as the
incident lightwave.
Thus, it has been known for many years that, due to
repulsive Coulombic interactions,
electrically charged macromolecules in an
aqueous
An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in wat ...
environment can exhibit long-range
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, forming a crystal lattice that extends in all directions. In addition, macros ...
-like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter. In all of these cases in nature, the same brilliant
iridescence (or play of colors) can be attributed to the diffraction and
constructive interference of visible lightwaves that satisfy
Bragg’s law, in a matter analogous to the
scattering
In physics, scattering is a wide range of physical processes where moving particles or radiation of some form, such as light or sound, are forced to deviate from a straight trajectory by localized non-uniformities (including particles and radiat ...
of
X-ray
An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...
s in crystalline solids.
The large number of experiments exploring the
physics
Physics is the scientific study of matter, its Elementary particle, fundamental constituents, its motion and behavior through space and time, and the related entities of energy and force. "Physical science is that department of knowledge whi ...
and
chemistry
Chemistry is the scientific study of the properties and behavior of matter. It is a physical science within the natural sciences that studies the chemical elements that make up matter and chemical compound, compounds made of atoms, molecules a ...
of these so-called "colloidal crystals" has emerged as a result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation.
In biology
Colloidal
phase separation is an important organising principle for compartmentalisation of both the
cytoplasm
The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
and Cell nucleus, nucleus of cells into biomolecular condensates—similar in importance to compartmentalisation via lipid bilayer biological membranes, membranes, a type of liquid crystal. The term biomolecular condensate has been used to refer to clusters of macromolecules that arise via liquid-liquid or liquid-solid
phase separation within cells. Macromolecular crowding strongly enhances colloidal phase separation and formation of biomolecular condensates.
In the environment
Colloidal particles can also serve as transport vectors
of diverse contaminants in the surface water (sea water, lakes, rivers, freshwater bodies) and in underground water circulating in fissured rocks
(e.g. limestone, sandstone, granite). Radionuclides and heavy metals easily sorption, sorb onto colloids suspended in water. Various types of colloids are recognised: inorganic colloids (e.g. clay particles, silicates, ferrihydrite, iron oxy-hydroxides), organic colloids (humic and fulvic substances). When heavy metals or radionuclides form pure colloids, the term "''eigencolloid''" is used to designate pure phases, i.e., pure Tc(OH)
4, U(OH)
4, or Am(OH)
3. Colloids have been suspected for the long-range transport of plutonium on the Nevada Nuclear Test Site. They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted
bentonite
Bentonite ( ) is an Absorption (chemistry), absorbent swelling clay consisting mostly of montmorillonite (a type of smectite) which can either be Na-montmorillonite or Ca-montmorillonite. Na-montmorillonite has a considerably greater swelli ...
s and in deep clay formations
because of the process of ultrafiltration occurring in dense clay membrane.
The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.
In soil science, the colloidal fraction in soils consists of tiny clay and humus
particles that are less than 1μm in diameter and carry either positive and/or negative Electric charge, electrostatic charges that vary depending on the chemical conditions of the soil sample, i.e. soil pH.
Intravenous therapy
Colloid solutions used in intravenous therapy belong to a major group of volume expanders, and can be used for intravenous fluid replacement. Colloids preserve a high colloid osmotic pressure in the blood,
and therefore, they should theoretically preferentially increase the intravascular volume, whereas other types of volume expanders called crystalloid solution, crystalloids also increase the interstitial volume and intracellular volume. However, there is still controversy to the actual difference in efficacy by this difference,
[ and much of the research related to this use of colloids is based on fraudulent research by Joachim Boldt.] Another difference is that crystalloids generally are much cheaper than colloids.[
]
References
{{Authority control
Colloids,
Chemical mixtures
Colloidal chemistry
Condensed matter physics
Soft matter
Dosage forms