A colloid is a heterogeneous system in which one substances is dispersed (dispersed phase) as very fine particles in another substances called dispersion medium.
The essential difference between a solution and a colloid is a that of particle size. While in a solution, the constituent particles are ions or small molecules, in a colloid, the dispersed phase may consist of polymer) or an aggregate of many atoms, ions or molecules. Colloidal particles are larger than simple molecules but small enough to remain suspended. Their range of diameters is between 1 and 190 nm.
Colloidal particles have an enormous surface area per unit mass as a result of their small size. Consider a cube with 1cm side.
The enormous surface area leads to some special properties of colloids to be discussed later in this article.
Classification of colloids
Colloids are classified on the basis of the following criteria:
- Physical state of dispersed phase and dispersion medium.
- Nature of interaction between dispersed phase and dispersed medium.
- Type of particles of dispersed phase.
Depending upon whether the dispersed phase and the dispersion medium are solid, luquids or gases, eight types of colloidal systems are possible. A gas mixed with another gas form a homogenous mixture and hence is not a colloidal system.
Many familiar commercial products and natural objective are colloids. For example, whipped cream 🍨 is a foam, which is a gas dispersed in a luquid. Firefighting foams, used at emergency airplane ✈️🛫 Landings are also colloidal systems. Most biological fluids are aqueous sold(solids dispersed in water).
Within a typical cell, proteins and nucleic acids are colloidal-size particles dispersed in an aqueous solution of ions and small molecules.
Out of the various types of colloids given in the most common are sols (solid in Liquids), gels luquid in solid) and emulsion (luquid in solid). However, in the present Unit we shall take up mentioned that if the dispersion medium in water, the sol is called aquasol or hydrosol and if dispersion medium is alcohol, it is called alcosol and so on.
Depending upon the nature of interaction between the dispersed phase and the dispersion medium, colloidal sols are divided into two categories, namely, lyophilic (solvent repelling) If water is the dispersion medium, the term used are hydrophilic and hydrophobic.
