Colloidal System 1k5z6c

1 1. Introduction: In1986 Thomas Graham which can work for diffusion to be found substances in sugars acids and bases. It can be parchment in a gelatin glue and albumen. These substances belongs to a category of crystalline state are known as crystalloids. Then the substance which belongs to another category is known as colloids. The branch of development the observation is called as a colloidal science. Colloids are mixtures whose particles are larger than the size of a molecule but smaller than particles that can be seen with the naked eye. Colloids are one of three major types of mixtures, the other two being solutions and suspensions. The three kinds of mixtures are distinguished by the size of the particles that make them up. The particles in a solution are about the size of molecules, approximately 1 nanometer in diameter. Those that make up suspensions are larger than 1,000 nanometers. Finally, colloidal particles range in size between 1 and 1,000 nanometers. Colloids are also called colloidal dispersions because the particles of which they are made are dispersed, or spread out, through the mixture. A full understanding of the properties of colloids calls upon a wide range of physical and chemical ideas, while the multitude of colloidal systems presented to us in nature, and familiar in modern society, exhibit a daunting complexity. It is this that has delayed the development of colloid science, since a detailed and fundamental theoretical understanding of colloidal behavior is possible only through a thorough knowledge of broad areas of physics, chemistry, and mathematical physics, together in many instances with an understanding of biological structures and processes. On the experimental side there is an everincreasing emphasis on the application of modern physical techniques to colloidal problems. Colloid science is thus a truly interdisciplinary subject.

2 2. The definition of colloid: Colloidal System is defined as the heterogenous biphasic system in which the dispersed phase ranges within 1-10 angstrom to few micrometers in dimensions. This dispersed phase is nothing but the colloidal particles or colloids. A colloidal system differs from other heterogenous and homogenous solutions in of the size of dispersed phase. e.g. - True solution has a size range of its dispersed phase less than 0.01 micrometre; while that of a heterogenous coarse dispersion varies between 10-1000 micrometres. Examples of pharmaceutical colloids--silver colloid (germicidal), Iron-dextran injection (official and used in treatment of anaemia istered intramuscularly), Iron-sorbitol injection (consists of citrate, sorbitol and dextran complexed to ferric ions) etc. 3. Characteristics of Colloids: 1) Particle Size 2) Particle Shape 3) Surface Area 4) Surface Charge

o Particle Size The particle size as stated above varies between 1-10 angstrom to few micrometres.However; the major consideration of the particle size in this context is the colour it reflects is mainly due to its size. Larger the particle size, lesser wavelength of

3 light it transmits. But this doesn't indicate that lesser particle size transmits larger wavelength of light. e.g. - Colloidal gold has a red color while that of a gold sol having intermediate sizes of gold particles has a violet color.

o Particle Shape The colloidal particles may possess different shapes like: 1)spherical (e.g.-surfactants) 2)rod-shaped(e.g.-Tobacco mosaic virus) 3)Flakes(e.g-Bentonite) 4)Ellipsoid(e.g.-serum albumin) 5)Branched(e.g.-cellulose) The shape of the particles also reflect specific colour. E.g-Gold colloid consisting of Spherical particles has red colour while those having disc shape have blue colour.

4 o Surface Area Since particle size is inversely proportional to surface area, colloids having smaller diameter have huge surface area. This is advantageous in the respect that it gears up some physical-chemical parameters associated with the system like it enhances solubility, absorption etc. o Surface Charge The surface charge occurs on colloidal particles mainly due to 2 reasons: 1) Presence of dissociable or associable functional groups (-COOH,-OH etc.) which on dissociation in a suitable solvent gives a negative charge to the surface of colloids. 2) Adsorption of ions onto the surface from the solvent. e.g. - Adsorption of H+ ions in dilute HCl solution or H+/OH- in aqueous medium The surface charge determines stability in the respect that presence of a huge amount of like charges creates repulsion among the colloidal particles thereby stabilizing the system. e.g. - Negatively charged colloids-sulphur, acacia,tragacanth Positively charged colloids-Aluminium,gelatin 4. Types of colloids: The followings are some of the importance types of colloids. 1. Lyophobic colloids 2. Lyophilic colloids 1. Lyophobic colloids: Lyophobic colloids are liquid hating colloids (Lyo means solvent and phobic means hating). When these colloids are mixed with the suitable liquid, very weak force of attraction exists between colloidal particles and liquid and system does not

5 into colloidal state readily. Therefore, lyophobic sols are difficult to prepare. Special techniques are employed to prepare these sols. 2. Lyophilic colloids: Lyophilic colloids are liquid loving colloids (Lyo means solvent and

philic means loving). When these colloids are mixed with the suitable liquid, high

force of attraction exists between colloidal particles and liquid. This result in formation of very stable solution called lyophilic sol. These sols are formed by substances like gums, starch and proteins. Lyophilic sol can be easily prepared by directly mixing colloid with the liquid.

5. The composition of colloids: Every colloid consists of two parts 1. Colloidal particles 2. The dispersing medium. The dispersing medium is the substance in which the colloidal particles are distributed. In muddy water, for example, the colloidal particles are tiny grains of sand, silt, and clay. The dispersing medium is the water in which these particles are suspended. Colloids can be made from almost any combination of gas, liquid, and solid. The particles of which the colloid is made are called the dispersed material. Any colloid consisting of a solid dispersed in a gas is called a smoke. A liquid dispersed in a gas is referred to as a fog. There are two phases in a colloidal system: Dispersed phase, the solute and dispersion medium, the Solvent. Various types of colloidal solutions, depending upon the dispersed phase and dispersion medium are:

6 Dispersed Phase

Dispersed Medium

Type of Colloid

Example

Gas

Liquid

Foam

Whipped cream, Soda water Froth

Gas

Solid

Solid Foam

Pumice stone, Foam Rubber

Liquid

Gas

Aerosol

Fog, Mist

Liquid

Liquid

Emulsion

Milk, Cod-Liver oil

Liquid

Solid

Solid Emulsion(gel)

Butter, Cheese, Jelly

Solid

Gas

Smoke

Soot in air, Dust

Solid

Liquid

Sol

Starch, Protein, Paint,

Solid

Solid

Solid Sol

Ruby glass, Alloys

6. Importance Functions of Colloids: 1. The followings are some of the importance functions of colloids. 2. They are intermediate between suspension and true solutions. 3. The colloids can be classified as dispersed phase and dispersed medium. 4. A dispersed phase has the substance of distributed in the colloidal particles. 5. The dispersed medium has continuous phase with a colloidal particles of dispersed. 6. It can be purified by an electro dialysis, dialysis and ultra filtration. 7. The lymphatic sols are prepared by special methods and these methods fall into two

7 categories as dispersion methods and condensation method. 8. In dispersion method they are splitting the coarse aggregates of a substance into a colloidal size. 9. The condensation methods can aggregate very small particles into the colloidal particles. 10. In the colloidal dispersions the suspended particles possess either in a positive or a negative charge. 11. The colloids have kinetic, optical and electrical property. 12. The colloidal substances are across in our daily life process as eating, wearing cloths, live in the house and reading news papers. 7. The application of colloids in various sectors: Colloids are substances, whose particle size is intermediate between a true solution and a suspension. There are much type of colloids, depending upon the state of dispersion medium as well as dispersed phase. There are a lot of applications of Colloids. Colloids play a very important role in everyday life as well as in agriculture, medicine, Biochemical use, etc. Some of the applications of Colloids are: Colloids have uses in our daily life as well as in various industrial processes. Some of the applications where colloids are present are listed below. 1) In medicine: Many medicines are either emulsions or colloidal suspensions as they are more effective on of their easy assimilation due to adsorption. o Argarol and protargol used as lotion are protected silver solutions. o Colloidal metals like gold, manganese, calcium etc. are used for intramuscular injection to raise the low vitality of the human system.

8 o Colloidal antimony is used in curing kalazar. o Colloidal sulphur is used as germ killer in plants. o Cod liver oil and halibut liver oil emulsions are good tonics. 2) Paint industry also uses colloids in the preparation of paints. 3) In purification of water: Alum in used for cleaning muddy water. River contains negatively charged clay particles. Alum is added to coagulate such colloidal impurities from water. Al+++ ions from alum neutralise the negative charge of the particles and bring them down as precipitate to the bottom. The clear water is decanted off. 4) In smoke precipitation: Smoke is a colloidal system in which carbon and other particles are the dispersed phase and air is a dispersion medium. In order to separate these particles, the smoke is ed through a column in which a positively charged metal ball hangs at the middle. The negatively charged carbon particles get neutralized and precipitate, releasing only hot air in the atmosphere. 5) Removal of dirt from sewage: Dirt is present in the form of negatively charged colloidal particles and hence is precipitated by an anode. 6) In rubber industry: Rubber is an emulsion of negatively charged particles in water. This emulsion is called Latex. In order to form a layer of rubber on some object, it is made into an anode in electrophoresis. The negatively charged particles of rubber get neutralized on the anode and deposit on it forming a layer. 7) Leather tanning: Hides have gel structure containing proteins in the colloidal state. It is a positively charged colloidal system. When hides are soaked in tannin, which is itself a negative solution, the mutual coagulation takes place between these two oppositely charged colloidal systems. This process is known as tanning. It hardens hides and stops their purification.

9 8) Delta formation: River water contains suspended particles of sand and sea water contains many electrolytes. When the river water meets sea water, the suspended particles of sand and the other colloidal impurities in the former are coagulated by the electrolytes of the later with the formation of delta. 9) In chemical warfare: Many harmful substances are sprayed by bomb or other means during war time. Gas masks containing colloidal animal charcoal are used in order to protect from them. It adsorbs such harmful gases and saves human life. 10) In nature: Colloids play a very important part in nature. The blue colour of the sky, pouring of rain, tail of comets, blood, and fertility of soils are all based on this phenomenon. 8. Pharmaceutical Applications of colloids: 1) Therapy: Colloidal system is used as therapeutic agents in different areas. e.g. - Silver colloid-germicidal Copper colloid-anticancer Mercury colloid-Antisyphilis 2) Stability: As already stated, charges play an important role in determining the stability of a colloidal system. Colloids, especially lyophobic colloids having like charges on particle surface repel each other and prevent flocculation in suspensions. e.g.- Colloidal dispersion of gelatin is used in coating over tablets and granules which upon drying leaves a uniform dry film over them and protect them from adverse conditions of the atmosphere. 3) Absorption: As colloidal dimensions are small enough, they have a huge surface area. Hence, the drug constituted colloidal form is released into the vicinity in large amount. e.g. - Sulphur colloid gives a large quantity of sulphur and this often leads to sulphur toxicity.

10 4) Dissolution --- Due to huge surface area, the dissolution rate is very large as stated by NoyesWhitney equation. dC/dT=DA(Cs-Cb)/Ln Where, D=dissolution coefficient dC/dT=Rate of diffusion A= surface area of particle Cs=concentration of stagnant layer (layer of solvent just adjacent to particle and is concentrated with the drug) Cb=concentration of bulk solution (Often dilute and represents the rest of the solvent in the system) L=length of stagnant layer n=viscosity of the medium 5) Targeted Drug Delivery: Liposomes are of colloidal dimensions and are preferentially taken up by the liver and spleen. Hence, principle of colloids is also used in targeted drug delivery system.

9. Applications of Colloids in Medicine Clarification: There are a lot of medicinal solutions, which are prepared as a colloid for their easy absorption by the human body. Water, from most drinking water bodies is slightly turbid in nature. This water may contain dissolved fine clay particles. The process of Coagulation of colloid is employed to clarify this type of water. Use of Aluminum sulfate, coagulates the clay particles, and clarifies water. Treatment of sewage water is also done by electrophoresis method employed in colloidal chemistry

11 10. Applications of Colloids - Industrial There are a lot of applications of colloids in industry. Lots of soaps and detergents are colloidal solutions. Similarly, paints, enamels, resins, gums are colloidal in nature. Lots of synthetic fibers like, Nylon, Terylene, etc employs the application of colloids for their preparation. Usually, the Cu wire comes coated with rubber, to prevent exposure. This rubber plating employs the application of colloid. Rubber, being negatively charged colloid, can be easily coated on metal (Cu wire.) Chrome tanning of leather also employs the technique of Colloids. Penetration of chromic acid, positively charged, on negative leather is Chrome tanning. This gives the leather its finish a. .Applications of Industrial Enzymes b. Industrial Applications of Coal

11. Miscellaneous applications of Colloids: Colloids are also used in the production of artificial rain by aggregation of small droplets of water. Clouds consist of small droplets of water dispersed in air. They are aggregated to form artificial rain. Formation of smokescreens is one of the good applications of colloids. This is brought about by Titanium dioxide dispersed in air. These are some of the major applications of colloidal solutions or colloids

12. Conclusion: colloids hold a very important place in our life. In fact, life itself is a whole protoplasmic structure and its reaction is colloidal. Applications of colloids are unlimited. Colloids find its applications in everyday life phenomena. The plant cells and animal tissues are made of protoplasm which is colloidal in nature and the blood that flows in our veins also a

12 colloid. Large numbers of food articles which we use in our daily life are colloidal in nature. For example, like starch, vegetable, fruits, milk, butter, cheese are colloidal in nature. We use a lot of jellies, jams, ice creams, etc and all these are colloidal solutions. Most of the medicines are colloidal in nature. Colloidal calcium and gold are istered by injections to raise the vitality of human system. Similarly, solutions, like, Calcium colloid are used for medicinal purposes. Colloids find another application in producing artificial rain. Cloud consists of charged particles of water dispersed in air. These particles are neutralized by spraying oppositely charged particles over a cloud. These neutralized particles of water combine to form large water drops. Thus, artificial rain is caused by the aggregation of minute particles of water to form large particles. After all we can say the importance of colloid in our life is so much.

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Reference

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Physical pharmacy-by Alfred Martin, 4th edition

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Essentials of Physical Pharmacy-by B.S.Bahl and G.D.Tuli

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http://mysite.du.edu/~jcalvert/phys/colloid.htm

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www.scienceclarified.com

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http://www.tutorvista.com/chemistry/types-of-colloids-and-

examples 

http://www.xamplified.com/applications-of-colloids