A Colloid or colloidal dispersion is a type of homogeneous mixture. A colloid consists of two separate phases: a dispersed phase and a continuous phase. In a colloid, the dispersed phase is made of tiny particles or droplets that are distributed evenly throughout the continuous phase. The size of the dispersed phase particles are between 1 nm and 1000 nm in at least one dimension. Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal foams, colloidal dispersions or hydrosols. The dispersed phase particles or droplets are largely affected by the surface chemistry present in the colloid. A mixture is a chemical substance which is a homogeneous or heterogeneous association without chemical bonding of chemical elements and/or chemical compounds in varying proportions and that retain their own individual properties and makeup. ... Surface chemistry is the study of chemical phenomena that occur at the interface of two phases, usually between a gas and a solid or between a liquid and a solid. ...

Because the size of the dispersed phase may be hard to measure, and because colloids look like solutions, colloids are sometimes characterized by their properties. For example, if a colloid has a solid phase dispersed in a liquid, the solid particles will not pass through a membrane, whereas the dissolved ions or molecules of a solution will pass through a membrane. In other words, dissolved components will diffuse through a membrane through which dispersed colloidal particles will not. diffusion (disambiguation). ...

Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color. Shot of sunbeams breaking through nebula bank The term Tyndall effect is usually applied to the effect of light scattering on particles in colloid systems, such as suspensions or emulsions. ...

Many familiar substances, including butter, milk, cream, aerosols (fog, smog, smoke), asphalt, inks, paints, glues, and sea foam are colloids. This field of study was introduced in 1861 by Scottish scientist Thomas Graham. Butter is commonly sold in sticks (pictured) or blocks, and frequently served with the use of a butter knife. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Asphalt is a sticky, black and highly viscous liquid or semi-solid that is present in most crude petroleums and in some natural deposits. ... “Glue” redirects here. ... Year 1861 (MDCCCLXI) was a common year starting on Tuesday (link will display the full calendar) of the Gregorian calendar (or a common year starting on Sunday of the 12-day slower Julian calendar). ... This article is about the country. ... Thomas Graham (December 21, 1805 – September 16, 1869) was born in Glasgow, Scotland. ...

Classification of colloids

Colloids can be classified as follows:

This article does not cite any references or sources. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... For other uses, see Solid (disambiguation). ... This article does not cite any references or sources. ... Particulates, alternatively referred to as particulate matter (PM), aerosols or fine particles, are tiny particles of solid or liquid suspended in a gas. ... Golden Gate Bridge in Fog Evening fog obscures Londons Tower Bridge from passers by. ... Dramatic morning mist Mist is a phenomenon of a liquid in small droplets floating through air. ... http://visibleearth. ... This article does not cite any references or sources. ... Particulates, alternately referred to as Particulate Matter (PM) , aerosols or fine particles are tiny particles of solid or liquid suspended in the air. ... A liquid will usually assume the shape of its container A liquid is one of the main states of matter. ... Sea foam on the beach Foam on a cappuccino Fire-retardant, foamed plastic being used as a temporary dam for firestop mortar in a cable penetration in a pulp and paper mill on Vancouver Island, British Columbia, Canada. ... Cans of cream. ... A. Two immisicible liquids, not emulsified; B. An emulsion of Phase B dispersed in Phase A; C. The unstable emulsion progressively separates; D. The surfactant (purple outline) positions itself on the interfaces between Phase A and Phase B, stabilizing the emulsion An emulsion is a mixture of two immiscible (unblendable... For the song by The Smashing Pumpkins, see Mayonaise (song). ... Sols are lyophobic (solvent hating) suspensions of solid particles (1-1000 nanometres in size) in a liquid. ... A glass of cows milk. ... This article does not cite any references or sources. ... An ink is a liquid containing various pigments and/or dyes used for coloring a surface to render an image or text. ... Human blood smear: a - erythrocytes; b - neutrophil; c - eosinophil; d - lymphocyte. ... For other uses, see Solid (disambiguation). ... This article or section is in need of attention from an expert on the subject. ... Styrofoam is a trademark name for polystyrene thermal insulation material, manufactured by Dow Chemical Company. ... // Specimen of highly porous pumice from Teide volcano on Tenerife, Canary Islands. ... In optical filters and theatrical lighting a color gel is a transparent or translucent colored panel used to change the color of transmitted light. ... Butter is commonly sold in sticks (pictured) or blocks, and frequently served with the use of a butter knife. ... Gelatin (also gelatine, from French gélatine) is a translucent brittle solid substance, colorless or slightly yellow, nearly tasteless and considered foul smelling, extracted from the collagen inside animals connective tissue. ... Cheese is a solid food made from the milk of cows, goats, sheep, and other mammals. ... For other OPAL articles, see Opal (disambiguation). ... Cranberry glass (or Gold Ruby glass as it is known in Europe) is a red glass made by adding gold chloride to the molten glass. ... Cranberry glass (or Gold Ruby glass as it is known in Europe) is a red glass made by adding gold(III) chloride to the molten glass. ...

Interaction between colloid 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 which 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, is short range and is attractive.
• Entropic forces: According to the second law of thermodynamics, a system progresses to a state in which entropy is maximized. This can result in effective forces even between hard spheres.
• Steric forces between polymer-covered surfaces or in solutions containing non-adsorbing polymer can modulate interparticle forces, producing an additional repulsive steric stabilization force or attractive depletion force between them.

In physics, Coulombs law is an inverse-square law indicating the magnitude and direction of electrical force that one stationary, electrically charged substance of small volume (ideally, a point source) exerts on another. ... In chemistry, the term van der Waals force originally referred to all forms of intermolecular forces; however, in modern usage it tends to refer to intermolecular forces that deal with forces due to the polarization of molecules. ... In physics, an entropic force acting in a system is a macroscopic force arising not as a result of an actual underlying microscopic force (such as electromagnetism), but as a statistical consequence of the whole systems tendency to increase its entropy. ...

Stabilization of a colloidal dispersion

Stabilization serves to prevent colloids from aggregating. Steric stabilization and electrostatic stabilization are the two main mechanisms for colloid stabilization. Electrostatic stabilization is based on the mutual repulsion of like electrical charges. Different phases generally have different charge affinities, so that a charge double-layer forms at any interface. Small particle sizes lead to enormous surface areas, and this effect is greatly amplified in colloids. In a stable colloid, mass of a dispersed phase is so low that its buoyancy or kinetic energy is too little to overcome the electrostatic repulsion between charged layers of the dispersing phase. The charge on the dispersed particles can be observed by applying an electric field: all particles migrate to the same electrode and therefore must all have the same sign charge! The DLVO theory is named after Derjaguin, Landau, Verwey and Overbeek who developed it in the 1940s. ... In physics, buoyancy is the upward force on an object produced by the surrounding fluid (i. ... The kinetic energy of an object is the extra energy which it possesses due to its motion. ...

Destabilizing a colloidal dispersion

Unstable colloidal dispersions form flocs as the particles aggregate due to interparticle attractions. In this way photonic glasses can be grown. This can be accomplished by a number of different methods: This article needs additional references or sources for verification. ...

• Removal of the electrostatic barrier that prevents aggregation of the particles. This can be accomplished by the addition of salt to a suspension or changing the pH of a suspension to effectively neutralize or "screen" the surface charge of the particles in suspension. This removes the repulsive forces that keep colloidal particles separate and allows for coagulation due to van der Waals forces.
• Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively charged colloidal silica particles can be flocculated by the addition of a positively charged polymer.
• Addition of nonadsorbed polymers called depletants that cause aggregation due to entropic effects.
• Physical deformation of the particle (e.g. stretching) may increase the van der Waals forces more than stabilization forces (such as electrostatic) resulting coagulation of colloids at certain orientations.

Unstable colloidal suspensions of low volume fraction form clustered liquid suspensions wherein individual clusters of particles fall to the bottom of the suspension (or float to the top if the particles are less dense than the suspending medium) once the clusters are of sufficient size for the Brownian forces that work to keep the particles in suspension to be overcome by gravitational forces. However, colloidal suspensions of higher volume fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels such as 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. Three different views of Brownian motion, with 32 steps, 256 steps, and 2048 steps denoted by progressively lighter colors. ... Modern toothpaste gel Toothpaste is a paste or gel dentifrice used to clean and improve the aesthetic appearance and health of teeth. ...

measuring intensity of colloids

the intensity of colloids can be measured by a UV-Visable spectophotometer.

Colloids as a model system for atoms

In physics, colloids are an interesting model system for atoms. Micron-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy. 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 that can be used to model ideal gases can be used to model the behavior of a hard sphere colloidal suspension. Additionally, phase transitions in colloidal suspensions can be studied in real time using optical techniques and are analogous to phase transitions in liquids. This is a discussion of a present category of science. ... For other uses, see Atom (disambiguation). ... Confocal microscopy is an imaging technique used to increase micrograph contrast and/or to reconstruct three-dimensional images by using a spatial pinhole to eliminate out-of-focus light or flare in specimens that are thicker than the focal plane. ...

Colloids in biology

In the early 20th century, before enzymology was well understood, colloids were thought to be the key to the operation of enzymes; i.e., the addition of small quantities of an enzyme to a quantity of water would, in some fashion yet to be specified, subtly alter the properties of the water so that it would break down the enzyme's specific substrate, such as a solution of ATPase breaking down ATP. Furthermore, life itself was explainable in terms of the aggregate properties of all the colloidal substances that make up an organism. As more detailed knowledge of biology and biochemistry developed, of course, the colloidal theory was replaced by the macromolecular theory, which explains an enzyme as a collection of identical huge molecules that act as very tiny machines, freely moving about between the water molecules of the solution and individually operating on the substrate, no more mysterious than a factory full of machinery. The properties of the water in the solution are not altered, other than the simple osmotic changes that would be caused by the presence of any solute. (19th century - 20th century - 21st century - more centuries) Decades: 1900s 1910s 1920s 1930s 1940s 1950s 1960s 1970s 1980s 1990s As a means of recording the passage of time, the 20th century was that century which lasted from 1901–2000 in the sense of the Gregorian calendar (1900–1999... Ribbon diagram of the catalytically perfect enzyme TIM. An enzyme is a protein that catalyzes, or speeds up, a chemical reaction. ... Ribbon diagram of the enzyme TIM, surrounded by the space-filling model of the protein. ... In biochemistry, a substrate is a molecule upon which an enzyme acts. ... ATPases are a class of enzymes that catalyze the decomposition of adenosine triphosphate (ATP) into adenosine diphosphate (ADP) and a free phosphate ion. ... Adenosine 5-triphosphate (ATP) is a multifunctional nucleotide that is most important as a molecular currency of intracellular energy transfer. ... For other uses, see Life (disambiguation). ... “Life on Earth” redirects here. ... Biology studies the variety of life (clockwise from top-left) E. coli, tree fern, gazelle, Goliath beetle Biology (from Greek: βίος, bio, life; and λόγος, logos, knowledge), also referred to as the biological sciences, is the study of living organisms utilizing the scientific method. ... Biochemistry is the study of the chemical processes and transformations in living organisms. ... A macromolecule is a large molecule with a large molecular mass bonded covalently, but generally the use of the term is restricted to polymers and molecules which structurally include polymers. ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... This article is about devices that perform tasks. ... This article or section does not cite any references or sources. ... Osmosis is the net movement of water across a partially permeable membrane from a region of high solvent potential to an area of low solvent potential, up a solute concentration gradient. ... A substance is soluble in a fluid if it dissolves in the fluid. ...

References

Chemistry The Central Science, 7th Ed. by Brown, Theodore, ISBN 013533480

See also

• Entropic force