Colloidal System

A mixed combination in which solute particles are greater than molecules or ions on the other hand cannot be seen by nude eye is called colloidal solution. An familiar mixture of two substances, one of which, called the dispersed phase, is regularly destruction the other handed in a outstandingly divided state through the second substance, called the dispersion Phase.

The dispersion Phase may be a gas, a liquid, or a solid and the dispersed phase may also be any of these, with the exclusion of one gas in another. A system of colloidal particles dispersed in a gas is called an aerosol. A colloid with water in dispersed phase is called a hydrosol. There is no severe line of differentiation between true solutions and colloidal systems or between mere holdups and colloidal systems. When the particles of the dispersed phase are smaller than about 10-3 µm in diameter, the system begins to assume the assets of a true solution; when the particles dispersed are much greater than 1 µm, departure of the dispersed phase from the dispersing Phase becomes so rapid that the system is best considered as a suspension. According to the latter criterion, natural clouds in the atmosphere should not be termed aerosols; however, since many cloud forms apparently show characteristics of true colloidal suspensions, this strict physical - chemical definition is often ignored for determinations of expedient and helpful analogy. Condensation nuclei and many not naturally smokes may be considered as aerosols.

The dispersion Phase may be a gas, a liquid, or a solid.

1. Smoke is composed of a solid dispersed in gas.

Milk is a liquid dispersed in liquid.

2. Pumice stone is a gas dispersed in solids.

There are two forms of colloidal systems.

1. Sol: A system composed of non-viscous colloidal solution is called sol. For example milk.
2. Gel: A system composed of viscid colloidal solution is called gel. For example on the other handter.

The colloidal system can be characterized into two general classes on the basis of their empathy for liquids:

Lyophilic System:

The system in which dispersed phase and liquid dispersion Phase draw each other is called lyophilic system.

Lyophobic System:

The system in which the dispersed phase and liquid dispersion phase repel each other is called lyophobic system.

Types of Colloidal Dispersions:

Dispersed phase and dispersion Phase can be solid, liquid or gas. Depending upon the state of dispersed phase and dispersion Phase, eight different types of colloidal dispersions can exist.

Eight Different Types of Colloidal Dispersions are:

Foam;

Solid foam;

Liquid;

Aerosol Emulsions;

Gels;

Solid;

Aerosol;

Sol;

Solid sol.

It is important to note that when one gas is mixed with another gas, a similar mixture is formed i.e. gases are completely miscible into each other. Colloidal dispersions are varied in nature and gas dispersed in another gaseous Phase does not form colloidal system. When the dispersion Phase is gas, the solution is called Aerosol and when the dispersion Phase is liquid, the colloidal dispersion is known as Sol. Sols can further be categorized into different types depending upon the liquid used.

• If the liquid used is water, the solution is Hydrosol or Aquasol.
• If liquid used is Benzene, solution is called Benzosol.
• If liquid used is Alcohol, the solution is Alcohol.
• If any organic compound is used, the solution is Organosol.

Properties of Colloidal System: The colloidal system shows following properties.

Adsorption: The affinity of molecules and ions to follow to the surface of certain solids or liquids is called adsorption. Colloidal particles show a high tendency of adsorption. Thus, colloidal system provides large surface area of adsorption of molecules and ions.

Brownian Movements: Robert Brown in1927 observed that colloidal particles show random dancing movements. These movements were named Brownian movements.

Tyndall Effect: The colloidal particles scatter light. This called Tyndall Effect. The path of light seems as a cone. It is known as Tyndall cone. This goods helps to detect the presence of colloidal particles.

Precipitation: The additions of an electrolyte remove the electrical double layer present around the colloidal particles. As a result the dispersed particles of a colloidal suspension will combined and precipitous.

Electrical Properties: All colloidal particles carry same electric charge. This charge may be positive or negative. There is adsorption of free ions in the dispersion Phase. It produces an electrical double layer around the colloidal particles. The electric charges on the colloidal particles calm down colloidal system.

Filtration: The colloidal particles cannot pass through a parchment membrane. This goods of colloidal dispersions is used to separate them from true solution by a process called dialysis.

Phase Reversal: The sol and gel form of colloidal system can be interchanged due to change in certain conditions. Certain lyophilic sols form gel under certain conditions. For example, aqueous agar sols are cooled. It forms a jelly—like gel. The conversion of a sol to a gel is called gelation. If a gel of gelation or agar is heated, it will convert back to a sol. This process is known as solution. The property of colloidal dispersions is called phase reversal.

Surface Charge: The most important characteristic of colloidal systems is surface charge on the particles. A particle is a group of bonded atoms or molecules. Charged particles repel each other, overpowering the tendency to collective and remaining dispersed.

Biological Significance of Colloidal Systems: Colloidal have following biological significance:

Protoplasm a colloidal system: Protoplasm a living, and viscous substance. It is surrounded by cell wall. It is present in prokaryotic and eukaryotic cells. Protoplasm is colloidal in nature. The small molecules and ions are true solute particles. On the other hand the larger particles remains postponed in water and form colloidal suspension or colloidal solution.

Cyclosis and amboeid movements: The cyclosis occurs due to phase reversal of colloidal property. The cyclosis usually occurs in sol phase. Amoeboid whereabouts in amoeba occur due to colloidal properties.

Fruits: Fruits store a large amount of protien and starch. They also show colloidal properties. These properties help in the storage of food in fruits.

Blood: The plasm protein forms a colloidal system in blood. This system maintains the pH and osmotic concentration of blood.

Milk: Milk is perfect colloidal system. It contains all necessary nutrients for young.