[Explained] 13 Applications of Colloids

Introduction to Colloids

The size of the particles of solution defines the nature of the solution. If the size of solute particles is less than 1 nm it will form true solutions but when the size is between 1 to 100 nm then it will form colloids. When the size of solute particles is greater than 100 nm it forms a suspension. It can be said that colloidal solution is an intermediate state between suspension and true solution.

Colloids are always heterogenous in nature and are made of two components, the dispersed phase and dispersion medium.

The substance present in the form of colloidal particles in a colloidal system constitutes the dispersed phase. Thus the dispersed phase may be defined as the phase constituting the colloidal particles.

For example, in a colloidal solution of ferric hydroxide in water the ferric hydroxide particles are of colloidal size and constitute the dispersed phase.

The medium in which the colloidal particles are dispersed is called dispersion medium. 

For example, in the colloidal solution of ferric hydroxide in water, water is the dispersion medium.

You can read more about:

Purification of Colloids

And also 

Various methods of preparing Colloids

Lets describe different types of colloids

Depending on the physical state of the dispersed phase and dispersed medium there are eight types of colloidal systems. 10 examples of colloids is given in the table below.

Sr. No	Dispersed Phase	Dispersion Medium	Common name of the system	Examples
1	Solid	Solid	Solid Sol	Gems, Ruby Glass, Colored Glass, Pigmented Plastics etc.
2	Solid	Liquid	Sol	Gold Sol, sulfur sol, ferric hydroxide sol, ink, most of the paints, starch dispersed in water, muddy water, cell fluids etc.
3	Solid	Gas	Aerosol of solids	Smoke, Dust etc.
4	Liquid	Solid	Gel	Cheese, butter, boot polish, jellies etc.
5	Liquid	Liquid	Emulsion	Milk, emulsified oils, medicines, hair cream etc.
6	Liquid	Gas	Aerosol of liquids	Fog, mist, clouds, Liquid sprays etc.
7	Gas	Solid	Solid Foam	Pumice stone, styrene foam, Foam rubber etc.
8	Gas	Liquid	Foam or Froth	Lemonade froth, soap lather, Shaving cream, foam, whipped cream etc.

How does Brownian movement stabilize colloidal solution?

Colloidal particles present in a colloidal solution exhibit a very important property called Brownian Movement. Colloidal particles are always seen continuously moving in a random zig zag movement under an ultra-microscope.

This random zig zag movement of colloidal particles known as Brownian movement prevents opposes the gravitational forces acting on colloidal particles and prevents them from settling down.

You can read about the properties of colloids in detail here:

Properties of Colloids

Importance of colloid in daily life.

Colloids play a very important role in our daily life and has uses in many industries. Some of the important applications of colloids are listed below.

1. Food
2. Medicine and Pharmacy
3. Purification of Water
4. Sewage Disposal
5. Smoke Precipitation
6. Artificial Rain
7. Rubber Industry
8. Leather Tanning
9. Cleansing Action of Soap
10. Smoke Screen 
11. Building Roads
12. Metallurgic Operations
13. Rocket Technology

We shall discuss each of them in detail.

Food 

Many of the food products are colloidal in nature. Milk, butter, whipped cream, fruit jellies. ice cream, bread are colloidal in nature to name a few. Milk is an emulsification of butter fat in water which is stabilized by casein which is a milk protein. Ice cream is a dispersion of colloidal ice particles in cream. Similarly, bread contains air dispersed in baked dough.

Field of medicine/pharmacy.

Why are they used in medicine?

Colloidal medicines are deemed to be very effective as they are very easily absorbed by the body system. Therefore, a large number of pharmaceutical preparations are emulsions. Halibut-liver oil, cod liver oil, skin ointments are few examples of emulsified medicines. Antibiotics such as penicillin, streptomycin etc. are usually injected in the body in the colloidal form. Several metal sols are also used as medicines.

Purification of Water

In water works, water is usually purified by the addition of certain electrolytes such as potash alum, aluminum sulfate, etc. This involves the phenomenon of coagulation. The impure water usually contains dispersed colloidal particles which can not be removed by filtration. When potash alum is added to the impure water, the negatively charged colloidal particles of impure particles get precipitated by the action of Al³⁺ ions furnished by the alum and can be removed by the filtration or decantation.

Sewage Disposal

Sewage water contains particles of dirt, mud, etc. which are colloidal in nature and carry some electrical charge. These particles may be removed by using the phenomenon of electrophoresis. The sewage water is passed through a a tunnel filled with metallic electrodes and maintained at high potential difference. 

The colloidal particles present in the sewage water migrate to the oppositely charged electrodes and get coagulated. This solves the problem of sewage disposal. Moreover, the dirt and mud or any impurity for that matter obtained on account of coagulation of colloidal dirt particles may be used as manure.

Smoke Precipitation

Smoke is colloidal system and consists of electrically charged colloidal particles of carbon dispersed in air. As smoke is a big source of pollution, it is always desirable to precipitate it. This means to say that it is always better to remove the colloidal carbon particles present in it. 

You might ask How does the precipitation of colloidal smoke take place in Cottrell precipitator?

Well, the removal of colloidal carbon particles from the smoke can be effected by using the phenomenon of electrophoresis. This is achieved in an apparatus called Cottrell precipitator. Smoke is allowed to pass through a chamber having a number of metal plates attached to a metal wire connected to a source of high potential (20000-70000 V). 

The electrically charged colloidal particles of carbon and dust gets discharged when come in contact with the oppositely charged plates and fall down to the bottom. The clean hot air leaves the precipitator from an exit near the top. This very well answers the questions,

Why is smoke from chimneys of industries passed through Cottrell precipitator, because it gives out pure dust free gases which then later go out into the atmosphere through the chimneys.

Artificial Rain

You might to be amazed to find this out but artificial rain is an application of colloids!

Clouds are colloidal systems and consists of water vapors mixed with dust particles. The water molecules present in a cloud develop some electrical charge. Therefore, clouds can be made into rain by neutralizing the charge present on colloidal particles (water molecules). 

This type of rain is called artificial rain and may be carried out by spraying oppositely charged colloidal dust or sand particles over a cloud. This neutralizes the charged particles on water molecules and compels them to get coagulated, which is to rain.

Rubber Industry

Latex obtained from rubber trees is an emulsion consisting of a dispersion of negatively charged rubber particles in water. In order to obtain rubber from latex, the latter is boiled when rubber particles get coagulated. The coagulated mass is vulcanized and sold as natural rubber.

Rubber plated articles can be prepared directly from latex by electrically depositing the negatively charged rubber particles over the article to be rubber plated by making the article an anode in the rubber plating bath.

Leather Tanning

During the tanning of leather, the positively charged colloidal particles of raw skin and hides are coagulated by the negatively charged tanning material which include tannin and compounds of aluminum and chromium. On soaking hides in the solutions of tanning materials, the coagulation of negatively charged tanning material takes place in the pores of hides and the latter get hardened.

Cleansing Action of Soaps

Soap solution is colloidal in nature and removes dirt and oil from clothes by forming water soluble emulsions.

Read more: Colloidal Properties of Soap

Smoke Screen

In chemical warfare, smoke screens are generally used to hide the movement of troops. Smokes screens are colloidal dispersion of very fine titanium oxide in air. Therefore, they are one of the uses of colloids.

Building Road

These days roads are built by asphalt emulsified in water. This technique does not require the necessity of melting the asphalt.

Metallurgical Operations 

Several metal ores are concentrated by froth flotation process. This process involves the treatment of the pulverized ore in the emulsion of pine oil.

Rocket Technology

Colloid thrusters are used in rocket engines. Thrusters propel the rockets. Colloid thrusters are a type of low thrust electric propulsion rocket engines that uses electrostatic acceleration of charged liquid droplets for propulsion.