A colloid is a type of mechanical mixture where one substance is dispersed evenly throughout another. In Chemistry, a mixture is a substance made by combining two or more different materials without a chemical reaction occurring (the objects do not bond together Because of this dispersal, some colloids have the appearance of solutions. In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances A colloidal system consists of two separate phases: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium). A colloidal system may be solid, liquid, or gaseous. A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of This page is about the physical properties of gas as a state of matter Many familiar substances are colloids, as shown in the below chart. A colloid is a type of mechanical Mixture where one substance is dispersed evenly throughout another

The dispersed-phase particles have a diameter of between approximately 5 and 200 nanometers. A nanometre ( American spelling: nanometer, symbol nm) ( Greek: νάνος nanos dwarf; μετρώ metrό count) is a ^[1] Such particles are normally invisible to an optical microscope, though their presence can be confirmed with the use of an ultramicroscope or an electron microscope. A microscope ( Greek: ( micron) = small + ( skopein) = to look or see is an instrument for viewing objects that are The ultramicroscope is a system of illumination for extremely small objects such as Colloidal particles Fog droplets or Smoke particles An electron microscope is a type of Microscope that uses Electrons to illuminate a specimen and create an enlarged image 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. Surface science is the study of physical and chemical phenomena that occur at the interface of two phases, including Solid - Liquid

Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. The Tyndall effect is an effect of light Scattering by colloidal particles or particles in suspension. Other colloids may be opaque or have a slight color.

Colloidal systems (also called colloidal solutions or colloidal suspensions) are the subject of interface and colloid science. Interface and colloid science is a branch of Chemistry dealing with Colloids Heterogeneous systems consisting of a mechanical mixture of particles between This field of study was introduced in 1861 by Scottish scientist Thomas Graham. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. Thomas Graham FRS ( December 21, 1805 – September 16, 1869) was born in Glasgow, Scotland.

Contents 1 Classification of colloids 2 Hydrocolloids 3 Interaction between colloid particles 4 Stabilization of a colloidal dispersion 5 Destabilizing a colloidal dispersion 6 Colloids as a model system for atoms 7 Colloids in biology 8 References 8.1 Notes 9 See also 10 External links

Classification of colloids

Because the size of the dispersed phase may be difficult to measure, and because colloids have the appearance of solutions, colloids are sometimes identified and characterized by their properties. For example, if a colloid consists of a solid phase dispersed in a liquid, the solid particles will not diffuse through a membrane, whereas with a solution the dissolved ions or molecules will diffuse through a membrane. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement

Colloids can be classified as follows:

		Dispersed Medium
		Gas	Liquid	Solid
Continuous Medium	Gas	NONE (All gases are mutually miscible)	Liquid Aerosol Examples: fog, mist, clouds	Solid Aerosol Examples: smoke, air particulates
	Liquid	Foam Examples: whipped cream	Emulsion Examples: milk, mayonnaise, hand cream	Sol Examples: paint, pigmented ink
	Solid	Solid Foam Examples: aerogel, styrofoam, pumice	Gel Examples: gelatin, jelly, cheese, opal	Solid Sol Examples: cranberry glass, ruby glass

In some cases, a colloid can be considered as a homogeneous, (not heterogeneous [meaning not the same]) mixture. This page is about the physical properties of gas as a state of matter Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. This page is about the physical properties of gas as a state of matter Miscibility is a term commonly used in Chemistry that refers to the property of Liquids to mix in all proportions forming a Homogeneous Solution Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Fog is a cloud that is in contact with the ground Stratus clouds are usually the only clouds that touch the ground Mist is a phenomenon of small droplets suspended in Air. It can occur as part of natural Weather or Volcanic activity and is common in cold air above A cloud is a visible mass of droplets or frozen crystals floating in the atmosphere above the surface of the Earth or another Planetary body Smoke is the collection of airborne solid and liquid Particulates and Gases ref> ''Smoke Production and Properties'' - SFPE Handbook of Fire Protection Engineering Particulates, alternatively referred to as particulate matter (PM or fine particles, are tiny particles of solid or liquid suspended in a gas Liquid is one of the principal States of matter. A liquid is a Fluid that has the particles loose and can freely form a distinct surface at the boundaries of The most general definition of foam is a substance that is formed by trapping many gas Bubbles in a Liquid or Solid. For the 1993 hip-hop single by the Wu-Tang Clan see CREAM CREAM is an acronym for Cognitive Reliability Error Analysis Method a An emulsion ( IPA: /ɪˈmʌlʃən/ is a mixture of two Immiscible (unblendable liquids Milk is an opaque white liquid produced by the Mammary glands of female Mammals (including Monotremes. Mayonnaise (sometime abbreviated to mayo in American English and other languages is a thick Condiment made primarily from Vegetable oil and Egg A sol is a Colloidal suspension of Solid particles (1-500 Nanometres in size in a Liquid. Paint is any Liquid, liquifiable or mastic composition which after application to a substrate in a thin layer is converted to an opaque Solid An ink is a Liquid containing various Pigments and/or Dyes used for coloring a surface to produce an Image, text, or A solid' object is in the States of matter characterized by resistance to Deformation and changes of Volume. Aerogel is a low-density solid-state material derived from Gel in which the liquid component of the gel has been replaced with gas Styrofoam is a trademark for polystyrene Thermal insulation, a material manufactured by Dow Chemical Company. Pumice is a textural term for a volcanic rock that is a solidified frothy lava composed of highly microvesicular glass Pyroclastic with very thin translucent A gel (from the lat gelu &mdashfreezing cold ice or gelatus &mdashfrozen immobile is an apparently solid jelly-like material formed from a Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the Cheese is a Food made from Milk, usually the milk of cows, Buffalo, Goats or sheep, by coagulation. OPAL ( Open Pool Australian Lightwater reactor) is a 20 megawatt pool-type nuclear research reactor that was officially opened in April 2007 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 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 This is because the distinction between "dissolved" and "particulate" matter can be sometimes a matter of approach.

Hydrocolloids

A hydrocolloid is defined as a colloid system wherein the colloid particles are dispersed in water. Water is a common Chemical substance that is essential for the survival of all known forms of Life. A hydrocolloid has colloid particles spread throughout water and depending on the quantity of water available can take on different states, e. g. , gel or sol (liquid). A gel (from the lat gelu &mdashfreezing cold ice or gelatus &mdashfrozen immobile is an apparently solid jelly-like material formed from a A sol is a Colloidal suspension of Solid particles (1-500 Nanometres in size in a Liquid. Hydrocolloids can be either irreversible (single-state) or reversible. For example, agar, a reversible hydrocolloid of seaweed extract, can exist in a gel and sol state, and alternate between states with the addition or elimination of heat. Agar or agar agar is a Gelatinous substance derived from Seaweed. Seaweed is a loose colloquial term encompassing macroscopic Multicellular, benthic marine Algae.

Many hydrocolloids are derived from natural sources. For example, carrageenan is extracted from seaweed, gelatin has bovine (cow) and fish origins, and pectin is extracted from citrus peel and apple pomace. Carrageenans or carrageenins (ˌkærəˈgiːnənz are a family of linear sulphated Polysaccharides extracted from red Seaweeds The name is derived from Gelatin (also gelatine, from French gélatine) is a translucent colourless brittle nearly tasteless solid substance, extracted from the The biological Subfamily bovines includes a diverse group of 10 species of medium to large sized Ungulates including domestic Cattle, Bison, Water Pectin (from Greek πηκτικός - pektikos, "congealed curdled" a white to light brown powder is a Heteropolysaccharide Citrus is a common term and Genus of Flowering plants in the family Rutaceae, originating in tropical and subtropical southeast regions of Pomace (pronounced /PUHM-is/ is the solid remains of Grapes Olives or other Fruit after pressing for juice or oil

Jell-O (trade mark Jell-O), the well-known dessert, is made from gelatin powder, another effective hydrocolloid. Jell-O is a Brand name belonging to USA -based Kraft Foods for a number of Gelatin desserts including fruit gels Puddings and no-bake Hydrocolloids are employed in food mainly to influence texture or viscosity (e. Mouthfeel is a product’s physical and Chemical interaction in the mouth Viscosity is a measure of the resistance of a Fluid which is being deformed by either Shear stress or Extensional stress. g. , a sauce).

Hydrocolloid-based medical dressings such as Duoderm are used for wound treatment and for acne. A dressing is an adjunct used by a person for application to a Wound in order to promote healing and/or prevent further harm Duoderm is an opaque dressing used in Medicine to protect Wounds from Contamination, and provide a moist wound-healing environment In Medicine, a wound is a type of Injury in which the Skin is torn cut or punctured (an open wound or where blunt force trauma

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. ---- Bold text Coulomb's law', developed in the 1780s by French physicist Charles Augustin de Coulomb, may be stated in scalar form 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. The Van der Waals equation is an Equation of state that can be derived from a special form of the potential between a pair of molecules (hard-sphere repulsion 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. In Physics, an entropic force acting in a system is a Macroscopic Force whose properties are primarily determined not by the character of a particular underlying 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 steric repulsive force (which is predominantly entropic in origin) or an attractive depletion force between them. See also Intramolecular forces ' Steric effects arise from the fact that each Atom within a Molecule occupies a certain

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. The DLVO theory is named after Derjaguin, Landau, Verwey and Overbeek who developed it in the 1940s 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. In Physics, buoyancy ( BrE IPA: /ˈbɔɪənsi/ is the upward Force on an object produced by the surrounding liquid or gas in which it is The kinetic energy of an object is the extra Energy which it possesses due to its motion 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!

Destabilizing a colloidal dispersion

Unstable colloidal dispersions form flocs as the particles aggregate due to interparticle attractions. Flocculation is a process where a Solute comes out of Solution in the form of floc or flakes In this way photonic glasses can be grown. This can be accomplished by a number of 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 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. This article is about the physical phenomenon for the stochastic process see Wiener process. 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. Toothpaste is a Paste or Gel Dentifrice used to clean and maintain the aesthetics and health of Teeth. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on the toothbrush after it is applied.

Colloids as a model system for atoms

In physics, colloids are an interesting model system for atoms. Physics (Greek Physis - φύσις in everyday terms is the Science of Matter and its motion. History See also Atomic theory, Atomism The concept that matter is composed of discrete units and cannot be divided into arbitrarily tiny Micron-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy. Confocal microscopy is an optical imaging technique used to increase Micrograph contrast and/or to Reconstruct three-dimensional Images by 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. The Movement for Democracy in Liberia (MODEL was a rebel group in Liberia that became active in March 2003, launching attacks from Côte d'Ivoire. In addition, phase transitions in colloidal suspensions can be studied in real time using optical techniques, and are analogous to phase transitions in liquids.

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. Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins Enzymes are Biomolecules that catalyze ( ie increase the rates of Chemical reactions Almost all enzymes are Proteins 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. ATPases are a class of Enzymes that catalyze the Decomposition of Adenosine triphosphate (ATP into Adenosine diphosphate (ADP and Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Furthermore, life itself was explainable in terms of the aggregate properties of all the colloidal substances that make up an organism. Life is a state that distinguishes Organisms from non-living objects such as non-life and dead organisms being manifested by growth through Metabolism As more detailed knowledge of biology and biochemistry developed, 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. Foundations of modern biology There are five unifying principles Biochemistry is the study of the chemical processes in living Organisms It deals with the Structure and function of cellular components such as The term macromolecule by definition implies "large Molecule " In Chemistry, a molecule is defined as a sufficiently stable electrically neutral group of at least two Atoms in a definite arrangement held together by A machine is any device that uses Energy to perform some activity A factory (previously manufactory) or manufacturing plant is an industrial Building where workers manufacture goods 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. Osmosis is the Diffusion of a solvent (frequently water through a semi-permeable membrane, from a solution of low solute concentration (high water potential In Chemistry, a solution is a Homogeneous Mixture composed of two or more substances

References

• Lyklema, J. Fundamentals of Interface and Colloid Science, vol. 2, page. 3. 208, 1995
• Hunter, R. J. Foundations of Colloid Science, Oxford University Press, 1989
• Dukhin, S. S. & Derjaguin, B. V. Electrokinetic Phenomena, J. Willey and Sons, 1974
• Russel, W. B. , Saville, D. A. and Schowalter, W. R. Colloidal Dispersions, Cambridge, 1989 University Press
• Kruyt, H. R. Colloid Science, Volume 1, Irreversible systems, Elsevier, 1959
• Dukhin, A. S. and Goetz, P. J. Ultrasound for characterizing colloids, Elsevier, 2002
• Rodil, Ma. Lourdes C. , Chemistry The Central Science, 7th Ed. ISBN 013533480

Notes

See also

• Entropic force

External links

• Hydrocolloid recipe collection

In Physics, an entropic force acting in a system is a Macroscopic Force whose properties are primarily determined not by the character of a particular underlying

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